Human T2R nucleic acid sequences

ABSTRACT

Newly identified mammalian taste-cell-specific G Protein-Coupled Receptors and the genes encoding said receptors are described. Specifically, T2R taste G Protein-Coupled Receptors that are believed to be involved in bitter taste sensation, and the genes encoding the same, are described, along with methods for isolating such genes and for isolating and expressing such receptors. Methods for representing taste perception of a particular tastant in a mammal are also described, as are methods for generating a novel molecules or combinations of molecules that elicit a predetermined taste perception in a mammal, and methods for simulating one or more tastes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. application Ser.No. 12/144,097 filed Jun. 23, 2008 (now U.S. Pat. No. 7,968,693), whichis a Continuation Application of U.S. application Ser. No. 10/986,871filed on Nov. 15, 2004 (now U.S. Pat. No. 7,396,651), which is aContinuation Application of U.S. application Ser. No. 09/825,882 filedApr. 5, 2001 (now U.S. Pat. No. 7,105,650), which claims priority toU.S. Provisional Application No. 60/195,532 filed Apr. 7, 2000, and U.S.Provisional Application No. 60/247,014 filed Nov. 13, 2000, which areincorporated by reference in their entireties.

FIELD OF THE INVENTION

The invention relates to newly identified mammalian chemosensory GProtein-Coupled Receptors, to a family of such receptors, and to thegenes and cDNA encoding said receptors. More particularly, the inventionrelates to newly identified mammalian chemosensory G Protein-CoupledReceptors active in taste signaling, to a family of such receptors, tothe genes and cDNA encoding said receptors, and to methods of using suchreceptors, genes, and cDNA in the analysis and discovery of tastemodulators.

DESCRIPTION OF THE RELATED ART

The taste system provides sensory information about the chemicalcomposition of the external world. Taste transduction is one of the mostsophisticated forms of chemical-triggered sensation in animals, and isfound throughout the animal kingdom, from simple metazoans to the mostcomplex of vertebrates. Mammals are believed to have five basic tastemodalities: sweet, bitter, sour, salty, and umami (the taste ofmonosodium glutamate).

Each taste modality is believed to be mediated by distinct transductionpathways. These pathways are believed to be mediated by receptors, e.g.,metabotropic or ionotropic receptors, expressed in subsets of tastereceptor cells. For instance, some tastes are believed to be mediated byG Protein-Coupled Receptors, while other tastes are believed to bemediated by channel proteins (see, e.g., Kawamura et al., Introductionto Umami: A Basic Taste (1987); Kinnamon et al., Ann. Rev. Physiol.,54:715-31 (1992); Lindemann, Physiol. Rev., 76:718-66 (1996); Stewart etal., Am. J. Physiol., 272:1-26 (1997)).

In mammals, taste receptor cells are assembled into taste buds that aredistributed into different papillae in the tongue epithelium.Circumvallate papillae, found at the very back of the tongue, containhundreds to thousands of taste buds. By contrast, foliate papillae,localized to the posterior lateral edge of the tongue, contain dozens tohundreds of taste buds. Further, fungiform papillae, located at thefront of the tongue, contain only a small number of taste buds.

Each taste bud, depending on the species, contains 50-150 cells,including precursor cells, support cells, and taste receptor cells. See,e.g., Lindemann, Physiol. Rev., 76:718-66 (1996). Receptor cells areinnervated at their base by afferent nerve endings that transmitinformation to the taste centers of the cortex through synapses in thebrain stem and thalamus. Elucidating the mechanisms of taste cellsignaling and information processing is important to understanding thefunction, regulation, and perception of the sense of taste.

Numerous physiological studies in animals have shown that taste receptorcells may selectively respond to different chemical stimuli (see, e.g.,Akabas et al., Science, 242:1047-50 (1988); Gilbertson et al., J. Gen.Physiol., 100:803-24 (1992); Bernhardt et al., J. Physiol., 490:325-36(1996); Cummings et al., J. Neurophysiol., 75:1256-63 (1996)). Moreparticularly, cells that express taste receptors, when exposed tocertain chemical stimuli, elicit taste sensation by depolarizing togenerate an action potential. The action potential is believed totrigger the release of neurotransmitters at gustatory afferent neuronsynapses, thereby initiating signaling along neuronal pathways thatmediate taste perception (see, e.g., Roper, Ann. Rev. Neurosci.,12:329-53 (1989)). Nonetheless, at present, the means by which tastesensations are elicited remains poorly understood (see, e.g.,Margolskee, BioEssays, 15:645-50 (1993); Avenet et al., J. MembraneBiol., 112:1-8 (1989)).

As described above, taste receptors specifically recognize moleculesthat elicit specific taste sensation. These molecules are also referredto herein as “tastants.” Many taste receptors belong to the7-transmembrane receptor superfamily (Hoon et al., Cell 96:451 (1999);Adler et al., Cell, 100:693 (2000)), which are also known as GProtein-Coupled Receptors (GPCRs). G Protein-Coupled ReCeptors controlmany physiological functions, such as endocrine function, exocrinefunction, heart rate, lipolysis, and carbohydrate metabolism. Thebiochemical analysis and molecular cloning of a number of such receptorshas revealed many basic principles regarding the function of thesereceptors.

For example, U.S. Pat. No. 5,691,188 describes how upon a ligand bindingto a GPCR, the receptor presumably undergoes a conformational changeleading to activation of the G Protein. G Proteins are comprised ofthree subunits: a guanyl nucleotide binding α subunit, a β subunit, anda γ subunit. G Proteins cycle between two forms, depending on whetherGDP or GTP is bound to the α subunit. When GDP is bound, the G Proteinexists as a heterotrimer: the Gαβγ complex. When GTP is bound, the αsubunit dissociates from the heterotrimer, leaving a Gβγ complex. When aGαβγ complex operatively associates with an activated G Protein-CoupledReceptor in a cell membrane, the rate of exchange of GTP for bound GDPis increased and the rate of dissociation of the bound Gα subunit fromthe Gαβγ complex increases. The free Gα subunit and Gβγ complex are thuscapable of transmitting a signal to downstream elements of a variety ofsignal transduction pathways. These events form the basis for amultiplicity of different cell signaling phenomena, including forexample the signaling phenomena that are identified as neurologicalsensory perceptions such as taste and/or smell.

Complete or partial sequences of numerous human and other eukaryoticchemosensory receptors are currently known (see, e.g., Pilpel, Y. etal., Protein Science, 8:969-77 (1999); Mombaerts, P., Annu. Rev.Neurosci., 22:487-50 (1999); EP0867508A2; U.S. Pat. No. 5,874,243; WO92/17585; WO 95/18140; WO 97/17444; WO 99/67282). Although much is knownabout the psychophysics and physiology of taste cell function, verylittle is known about the molecules and pathways that mediate itssensory signaling response. The identification and isolation of noveltaste receptors and taste signaling molecules could allow for newmethods of chemical and genetic modulation of taste transductionpathways. For example, the availability of receptor and channelmolecules could permit screening for high affinity agonists,antagonists, inverse agonists, and modulators of taste activity. Suchtaste modulating compounds could be useful in the pharmaceutical andfood industries to improve the taste of a variety of consumer products,or to block undesirable tastes, e.g. bitter tastes, in certain products.

SUMMARY OF THE INVENTION

In part, the present invention addresses the need for betterunderstanding of the interactions between chemosensory receptors andchemical stimuli. Thus, the present invention provides, among otherthings, novel taste receptors, and methods for utilizing such receptors,and the genes and cDNAs encoding such receptors, to identify moleculesthat can be used to modulate taste transduction.

More particularly, the invention relates to a recently discovered familyof G Protein-Coupled Receptors, and to the genes and cDNAs encoding saidreceptors. The receptors are thought to be primarily involved in bittertaste transduction, but can be involved in transducing signals fromother taste modalities as well.

The invention provides methods for representing the perception of tasteand/or for predicting the perception of taste in a mammal, including ina human. Preferably, such methods may be performed by using thereceptors and genes encoding said receptors disclosed herein.

Toward that end, it is an object of the invention to provide a newfamily of mammalian G Protein-Coupled Receptors, herein referred to asT2Rs, active in taste perception. It is another object of the inventionto provide fragments and variants of such T2Rs that retaintastant-binding activity.

It is yet another object of the invention to provide nucleic acidsequences or molecules that encode such T2Rs, fragments, or variantsthereof.

It is still another object of the invention to provide expressionvectors which include nucleic acid sequences that encode such T2Rs, orfragments or variants thereof, which are operably linked to at least oneregulatory sequence such as a promoter, enhancer, or other sequenceinvolved in positive or negative gene transcription and/or translation.

It is still another object of the invention to provide human ornon-human cells that functionally express at least one of such T2Rs, orfragments or variants thereof.

It is still another object of the invention to provide T2R fusionproteins or polypeptides that include at least a fragment of at leastone of such T2Rs.

It is another object of the invention to provide an isolated nucleicacid molecule encoding a T2R polypeptide comprising a nucleic acidsequence that is at least 50%, preferably 75%, 85%, 90%, 95%, 96%, 97%,98%, or 99% identical to a nucleic acid sequence selected from the groupconsisting of: SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 23,and conservatively modified variants thereof.

It is a further object of the invention to provide an isolated nucleicacid molecule comprising a nucleic acid sequence that encodes apolypeptide having an amino acid sequence at least 35 to 50%, andpreferably 60%, 75%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical toan amino acid sequence selected from the group consisting of: SEQ IDNOS: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, and 24, and conservativelymodified variants thereof, wherein the fragment is at least 20,preferably 40, 60, 80, 100, 150, 200, or 250 amino acids in length.Optionally, the fragment can be an antigenic fragment that binds to ananti-T2R antibody.

It is still a further object of the invention to provide an isolatedpolypeptide comprising a variant of said fragment, wherein there is avariation in at most 10, preferably 5, 4, 3, 2, or 1 amino acidresidues.

It is still another object of the invention to provide agonists orantagonists of such T2Rs, or fragments or variants thereof.

It is yet another object of the invention to provide methods forrepresenting the perception of taste and/or for predicting theperception of taste in a mammal, including in a human. Preferably, suchmethods may be performed by using the T2Rs, or fragments or variantsthereof, and genes encoding such T2Rs, or fragments or variants thereof,disclosed herein.

It is yet another object of the invention to provide novel molecules orcombinations of molecules that elicit a predetermined taste perceptionin a mammal. Such molecules or compositions can be generated bydetermining a value of taste perception in a mammal for a known moleculeor combinations of molecules; determining a value of taste perception ina mammal for one or more unknown molecules or combinations of molecules;comparing the value of taste perception in a mammal for one or moreunknown compositions to the value of taste perception in a mammal forone or more known compositions; selecting a molecule or combination ofmolecules that elicits a predetermined taste perception in a mammal; andcombining two or more unknown molecules or combinations of molecules toform a molecule or combination of molecules that elicits a predeterminedtaste perception in a mammal. The combining step yields a singlemolecule or a combination of molecules that elicits a predeterminedtaste perception in a mammal.

It is still a further object of the invention to provide a method ofscreening one or more compounds for the presence of a taste detectableby a mammal, comprising: a step of contacting said one or more compoundswith at least one of the disclosed T2Rs, fragments or variants thereof,preferably wherein the mammal is a human.

It is another object of the invention to provided a method forsimulating a taste, comprising the steps of: for each of a plurality ofT2Rs, or fragments of variants thereof disclosed herein, preferablyhuman T2Rs, ascertaining the extent to which the T2R interacts with thetastant; and combining a plurality of compounds, each having apreviously ascertained interaction with one or more of the T2Rs, inamounts that together provide a receptor-stimulation profile that mimicsthe profile for the taste. Interaction of a tastant with a T2R can bedetermined using any of the binding or reporter assays described herein.The plurality of compounds may then be combined to form a mixture. Ifdesired, one or more of the plurality of the compounds can be combinedcovalently. The combined compounds substantially stimulate at least 50%,60%, 70%, 75%, 80% or 90% or all of the receptors that are substantiallystimulated by the tastant.

In yet another aspect of the invention, a method is provided wherein aplurality of standard compounds are tested against a plurality of T2Rs,or fragments or variants thereof, to ascertain the extent to which theT2Rs each interact with each standard compound, thereby generating areceptor stimulation profile for each standard compound. These receptorstimulation profiles may then be stored in a relational database on adata storage medium. The method may further comprise providing a desiredreceptor-stimulation profile for a taste; comparing the desired receptorstimulation profile to the relational database; and ascertaining one ormore combinations of standard compounds that most closely match thedesired receptor-stimulation profile. The method may further comprisecombining standard compounds in one or more of the ascertainedcombinations to simulate the taste.

It is a further object of the invention to provide a method forrepresenting taste perception of a particular substance in a mammal,comprising the steps of: providing values X₁ to X_(n) representative ofthe quantitative stimulation of each of n T2Rs of said vertebrate, wheren is greater than or equal to 4, n is greater than or equal to 12; n isgreater than or equal to 24, or n is greater than or equal to 40; andgenerating from said values a quantitative representation of tasteperception. The T2Rs may be a taste receptor disclosed herein, orfragments or variants thereof, the representation may constitute a pointor a volume in n-dimensional space, may constitute a graph or aspectrum, or may constitute a matrix of quantitative representations.Also, the providing step may comprise contacting a plurality ofrecombinantly produced T2Rs, or fragments or variants thereof, with atest composition and quantitatively measuring the interaction of saidcomposition with said receptors.

It is a related object of the invention to provide a method forpredicting the taste perception in a mammal generated by one or moremolecules or combinations of molecules yielding unknown taste perceptionin a mammal, comprising the steps of: providing values X₁ to X_(n)representative of the quantitative stimulation of each of n T2Rs of saidvertebrate, where n is greater than or equal to 4 n is greater than orequal to 12; n is greater than or equal to 24, or n is greater than orequal to 40; for one or more molecules or combinations of moleculesyielding known taste perception in a mammal; and generating from saidvalues a quantitative representation of taste perception in a mammal forthe one or more molecules or combinations of molecules yielding knowntaste perception in a mammal, providing values X₁ to X_(n)representative of the quantitative stimulation of each of n T2Rs of saidvertebrate, where n is greater than or equal to 4, n is greater than orequal to 12; n is greater than or equal to 24, or n is greater than orequal to 40; for one or more molecules or combinations of moleculesyielding unknown taste perception in a mammal; and generating from saidvalues a quantitative representation of taste perception in a mammal forthe one or more molecules or combinations of molecules yielding unknowntaste perception in a mammal, and predicting the taste perception in amammal generated by one or more molecules or combinations of moleculesyielding unknown taste perception in a mammal by comparing thequantitative representation of taste perception in a mammal for the oneor more molecules or combinations of molecules yielding unknown tasteperception in a mammal to the quantitative representation of tasteperception in a mammal for the one or more molecules or combinations ofmolecules yielding known taste perception in a mammal. The T2Rs used inthis method may include a taste receptor, or fragment or variantthereof, disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention thus provides isolated nucleic acid molecules encodingtaste-cell-specific G Protein-Coupled Receptors (“GPCRs”), and thepolypeptides they encode. These nucleic acid molecules and thepolypeptides that they encode are members of the T2R family oftaste-cell-specific GPCRs. More particularly, the recent identificationof the T2R gene family, which encodes candidate bitter taste receptors,database accession numbers AF227129-AF227149 and AF240765-AF240768,prompted the search for, and identification of related genes in publicnucleotide sequence databases. The present invention relates to newlyidentified members of this family. Further information regarding the T2Rfamily can be found in Adler et al., Cell, 100:693-702 (2000) andChandrashekar et al., Cell, 100:703-11 (200), both of which are hereinincorporated by reference in their entireties.

Nucleic acids encoding the T2R proteins and polypeptides of theinvention can be isolated from a variety of sources, geneticallyengineered, amplified, synthesized, and/or expressed recombinantlyaccording to the methods disclosed in WO 0035374, which is hereinincorporated by reference in its entirety.

More particularly, the invention provides nucleic acids encoding a novelfamily of taste-cell-specific G Protein-Coupled Receptors. These nucleicacids and the receptors that they encode are referred to as members ofthe “T2R” family of taste-cell-specific G Protein-Coupled Receptors(“GPCRs”). These taste-cell-specific GPCRs are believed to be componentsof the taste transduction pathway, specifically, the bitter tastetransduction pathway, and are involved in the taste detection ofsubstances such as the bitter substances, 6-n-propylthiouracil (PROP),sucrose octaacetate (soa), raffinose undecaacetate (rua), denatonium,copper glycinate, and quinine. However, the T2Rs may be involved inother taste modalities as well.

Further, it is believed that T2R family members may act in combinationwith other T2R family members, other taste-cell-specific GPCRs, or acombination thereof, to thereby effect chemosensory taste transduction.For instance, it is believed that T2R family members maybe co-expressedwithin the same taste receptor cell type, and the co-expressed receptorsmay physically interact to form a heterodimeric taste receptor.Alternatively, the co-expressed receptors may both independently bind tothe same type of ligand, and their combined binding may result in aspecific perceived taste sensation.

The invention also provides methods of screening for modulators, e.g.,activators, inhibitors, stimulators, enhancers, agonists, andantagonists, of these novel taste-cell-specific GPCRs. Such modulatorsof taste transduction are useful for pharmacological and geneticmodulation of taste signaling pathways. These methods of screening canbe used to identify high affinity agonists and antagonists of taste cellactivity. These modulatory compounds can then be used in the food andpharmaceutical industries to customize taste, for example, to decreaseor mask the bitter taste of foods or drugs.

Thus, the invention provides assays for taste modulation, where membersof the T2R family act as direct or indirect reporter molecules of theeffect of modulators on taste transduction. GPCRs can be used in assays,e.g., to measure changes in ligand binding, ion concentration, membranepotential, current flow, ion flux, transcription, signal transduction,receptor-ligand interactions, second messenger concentrations, in vitro,in vivo, and ex vivo. In one embodiment, members of the T2R family canbe used as indirect reporters via attachment to a second reportermolecule such as green fluorescent protein (see, e.g., Mistili &Spector, Nature Biotechnology, 15:961-64 (1997)). In another embodiment,T2R family members are recombinantly expressed in cells, and modulationof taste transduction via GPCR activity can be assayed by measuringchanges in Ca²⁺ levels and other intracellular messengers such as cAMP,cGMP, or IP3.

In a preferred embodiment, a T2R polypeptide is expressed in aneukaryotic cell as a chimeric receptor with a heterologous sequence thatfacilitates plasma membrane trafficking or maturation and targetingthrough the secretory pathway. In a preferred embodiment, theheterologous sequence is a rhodopsin sequence, such as an N-terminalfragment of a rhodopsin. Such chimeric T2R receptors can be expressed inany eukaryotic cell, such as HEK-293 cells. Preferably, the cellscomprise a functional G Protein, e.g., Gα15, that is capable of couplingthe chimeric receptor to an intracellular signaling pathway or to asignaling protein such as phospholipase C. Activation of such chimericreceptors in such cells can be detected using any standard method, suchas by detecting changes in intracellular calcium by detectingFURA-2-dependent fluorescence in the cell. If host cells do not expressan appropriate G Protein, they may be transfected with a gene encoding apromiscuous G Protein such as those described in U.S. Ser. No.60/243,770, which is herein incorporated by reference in its entirety.

Methods of assaying for modulators of taste transduction can include invitro ligand binding assays using T2R polypeptides, portions thereof,such as the extracellular domain, transmembrane region, or combinationsthereof, or chimeric proteins comprising one or more domains of a T2Rfamily member; oocyte, primary cell or tissue culture cell T2R geneexpression, or expression of T2R fragments or fusion proteins, such asrhodopsin fusion proteins; phosphorylation and dephosphorylation of T2Rfamily members; G Protein binding to GPCRs; arrestin binding;internalization; ligand binding assays; voltage, membrane potential andconductance changes; ion flux assays; changes in intracellular secondmessengers such as cGMP, cAMP and IP3; changes in intracellular Ca²⁺levels; and neurotransmitter release.

Further, the invention provides methods of detecting T2R nucleic acidand protein expression, allowing investigation of taste transductionregulation and specific identification of taste receptor cells. T2Rfamily members also provide useful nucleic acid probes for paternity andforensic investigations. T2R genes are also useful as a nucleic acidprobes for identifying taste receptor cells, such as foliate, fungiform,circumvallate, geschmackstreifen, and epiglottis taste receptor cells,in particular bitter-taste receptive, gustducin expressing cells.Furthermore, the nucleic acids and the polypeptides they encode can beused as probes to dissect taste-induced behaviors.

T2R polypeptides can also be used to generate monoclonal and polyclonalantibodies useful for identifying taste receptor cells. Taste receptorcells can be identified using techniques such as reverse transcriptionand amplification of mRNA, isolation of total RNA or poly A+ RNA,northern blotting, dot blotting, in situ hybridization, RNaseprotection, S1 digestion, probing DNA microchip arrays, western blots,and the like.

The T2R genes and the polypeptides they encode comprise a family ofrelated taste-cell-specific G Protein-Coupled Receptors. Within thegenome, these genes are present either alone or within one of severalgene clusters. One gene cluster, located at human genomic region 12p13,comprises at least 24 genes, and a second cluster, located at 7q33,comprises at least 7 genes. In total, more than 60 distinct T2R familymembers have been identified from difference organisms, includingseveral putative pseudogenes. It is estimated that the human genome mayinclude approximately 40 distinct T2R genes, encoding about 30functional human receptors.

Some of the T2R genes have been associated with previously mapped lociimplicated in the control of bitter taste. For example, the human T2R1is located at human interval 5p15, precisely where a locus thatinfluences the ability to taste the substance PROP has previously beenmapped (see Reed et al., Am. Hum. Genet., 64:1478-80 (1999)). Inaddition, the human gene cluster found at genomic region 12p13corresponds to a region of mouse chromosome 6 that has been shown tocontain numerous bitter-tasting genes, that are believed to influencetaste perception or sensation including e.g., sucrose octaacetate,raffinose, undecaacetate cycloheximide, and quinine (see, e.g., Lush etal., Genet. Res., 6:167-74 (1995)). These associations suggest that theT2R genes are involved in the taste detection of various substances, inparticular bitter substances. In addition, mouse T2R5 is specificallyreceptive to cycloheximide, and mutations in the mT2R5 gene have beenhypothesized to produce a cycloheximide-non-tasting phenotype.Similarly, human T2R4 and mouse T2R8 are specifically responsive to bothdenatonium and PROP.

Functionally, the T2R genes comprise a family of related seventransmembrane G Protein-Coupled Receptors which are believed to beinvolved in taste transduction and which may interact with a G Proteinto mediate taste signal transduction (see, e.g., Fong, Cell Signal,8:217 (1996); Baldwin, Curr. Opin. Cell Biol., 6:180 (1994)). Inparticular, T2Rs are believed to interact in a ligand-specific mannerwith the G Protein gustducin.

Structurally, the nucleotide sequences of T2R family members encode afamily of related polypeptides comprising an extracellular domain, seventransmembrane domains, and a cytoplasmic domain. Related T2R familygenes from other species typically will share about 20-30% nucleotidesequence identity over a region of at least about 50 nucleotides inlength, optionally 100, 200, 500, or more nucleotides in length to SEQID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 23, or conservativelymodified variants thereof; or encode polypeptides sharing at least about30-40% amino acid sequence identity over an amino acid region at leastabout 25 amino acids in length, optionally 50 to 100 amino acids inlength to SEQ ID NOS: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, and 24, orconservatively modified variants thereof. It has been shown that T2Rgenes are selectively expressed in subsets of taste receptor cells ofthe tongue, palate epithelium, foliate, geschmackstreifen, andepiglottis. In contrast, studies have shown that T2Rs are less oftenexpressed in fungiform papillae. Further, it has been shown that T2Rsare selectively expressed in gustducin-positive cells.

Several consensus amino acid sequences or domains have also beenidentified that are characteristic of T2R family members. Particularly,it has been found that T2R family members typically comprise a sequencehaving at least about 50%, optionally 55%, 60%, 65%, 70%, 75%, 80%, 85%,90%, 95%, or higher, identity to T2R Transmembrane Region I, T2RTransmembrane Region II, T2R Transmembrane Region III, T2R TransmembraneRegion IV, T2R Transmembrane Region V, and T2R Transmembrane Region VII.These conserved domains thus can be used to identify members of the T2Rfamily, by identity, specific hybridization or amplification, orspecific binding by antibodies raised against a domain. Such T2Rtransmembrane regions have the following amino acid sequences:

T2R Family Consensus Sequence 1: (SEQ ID NO: 25)E(F/A)(I/V/L)(V/L)G(I/V)(L/V)GN(G/T)FI(V/A) LVNC(I/M)DWT2R Family Consensus Sequence 2: (SEQ ID NO: 26)(D/G)(F/L)(I/L)L(T/I)(G/A/S)LAISRI(C/G/F)LT2R Family Consensus Sequence 3: (SEQ ID NO: 27)NH(L/F)(S/T/N)(L/I/V)W(F/L)(A/T)T(C/S/N)L (S/N/G)(I/V)T2R Family Consensus Sequence 4: (SEQ ID NO: 28)FY(F/C)LKIA(N/S)FS(H/N)(P/S)(L/I/V)FL(W/Y)LKT2R Family Consensus Sequence 5: (SEQ ID NO: 29)LLI(I/F/V)SLW(K/R)H(S/T)(K/R)(Q/K)(M/I)(Q/K)T2R Family Consensus Sequence 6: (SEQ ID NO: 30)HS(F/L)(I/V)LI(L/M)(G/S/T)N(P/S/N)KL(K/R)(Q/R)

Specific regions of human T2R nucleotide and amino acid sequences may beused to identify polymorphic variants or alleles or homologs comprisedin humans or other species. This identification can be effected invitro, e.g., under stringent hybridization conditions or PCR (e.g.,using primers encoding the T2R consensus sequences identified above) andsequencing, or by using the sequence information in a computer systemfor comparison with other nucleotide sequences. Typically,identification of polymorphic variants or alleles of T2R family memberscan be made by comparing an amino acid sequence of about 25 amino acidsor more, e.g., 50-100 amino acids. Amino acid identity of approximately30-40%, optionally 50-60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95-99% orabove suggests that a protein is a polymorphic variant, or allele, or ahomolog or ortholog of a T2R family member. Sequence identity can becalculated by the methods disclosed infra. It can be determined almostdefinitely that a positive T2R gene falls within the T2R family based onthe additional presence of at least one conserved sequence that isidentical or at least 75% identical to the previously identified T2Rfamily consensus sequences. Sequence comparison can be performed usingany of the sequence comparison algorithms discussed below. Antibodiesthat bind specifically to T2R polypeptides or a conserved region thereofcan also be used to identify alleles, interspecies homologs, andpolymorphic variants of T2R proteins.

Polymorphic variants, or alleles, and related T2R homologs or orthologscan be confirmed by examining taste-cell-specific expression of theputative T2R polypeptide. Typically, T2R polypeptides having an aminoacid sequence disclosed herein can be used as a positive control incomparison to the putative T2R protein to demonstrate the identificationof an allele or homolog of the T2R family member. Such homologs oralleles will similarly posses the seven transmembrane structure of a GProtein-Coupled Receptor.

Nucleotide and amino acid sequence information for T2R family membersmay also be used to construct models of taste-cell-specific polypeptidesin a computer system. These models are subsequently used to identifycompounds that can activate or inhibit T2R receptor proteins. Suchcompounds that modulate the activity of T2R family members can be usedto investigate the role of T2R genes and polypeptides in tastetransduction.

The isolation of T2R family members provides a means for assaying forinhibitors and activators of taste transduction. Biologically active T2Rproteins are useful for testing inhibitors and activators of T2R astaste transducers, especially bitter taste transducers, using in vivo(animal based assays) and in vitro assays that measure, e.g., ligandbinding; phosphorylation and dephosphorylation; binding to G Proteins; GProtein activation; regulatory molecule binding; voltage, membranepotential and conductance Changes; ion flux; intracellular secondmessengers such as cGMP, cAMP, IP3; and intracellular calcium levels.Such activators and inhibitors identified using T2R family members canbe used to further study taste transduction and to identify specifictaste agonists and antagonists. Such activators and inhibitors areuseful as pharmaceutical and food agents for customizing taste, forexample to decrease the bitter taste of foods or pharmaceuticals.

The present invention also provides assays, preferably high throughputassays, to identify molecules that interact with and/or modulate a T2Rpolypeptide. In numerous assays, a particular portion of a T2R familymember will be used, e.g., an extracellular, transmembrane, orintracellular or region. In numerous embodiments, an extracellulardomain, transmembrane region, or combination thereof is bound to a solidsubstrate, and used, e.g., to isolate ligands, agonists, inverseagonists, antagonists, or any other molecules that can bind to and/ormodulate the activity of an extracellular or transmembrane region of aT2R polypeptide.

In certain embodiments, a region of a T2R polypeptide, e.g., anextracellular, transmembrane, or intracellular region, is fused to aheterologous polypeptide, thereby forming a chimeric polypeptide, e.g.,a chimeric polypeptide with GPCR activity. Such chimeric polypeptidesare useful, e.g., in assays to identify ligands, agonists, inverseagonists, antagonists, or other modulators of a T2R polypeptide. Inaddition, such chimeric polypeptides are useful to create novel tastereceptors with novel ligand binding specificity, modes of regulation,signal transduction pathways, or other such properties, or to createnovel taste receptors with novel combinations of ligand bindingspecificity, modes of regulation, signal transduction pathways, etc.Also T2R nucleic acids and expression of T2R polypeptides can be used tocreate topological maps of the tongue that potentially can be used tostudy the relation of tongue taste receptor cells to taste sensoryneurons in the brain. In particular, methods of detecting T2Rs canpotentially be used to identify taste cells that are sensitive to bittertasting substances. Chromosome localization of the genes encoding humanT2R genes can also potentially be used to identify diseases, mutations,and traits caused by, or associated with T2R family members.

Generally, the invention provides isolated nucleic acid molecules of theT2R gene family and the taste receptors they encode. The presentinvention also includes not only nucleic acid and polypeptide sequenceshaving the specified amino acid sequences, but also fragments,particularly fragments of, for example, 40, 60, 80, 100, 150, 200, or250 nucleotides, or more, as well as protein fragments of, for example,10, 20, 30, 50, 70, 100, or 150 amino acids, or more.

Various conservative mutations and substitutions are envisioned to bewithin the scope of the invention. For instance, it would be within thelevel of skill in the art to perform amino acid substitutions usingknown protocols of recombinant gene technology including PCR, genecloning, site-directed mutagenesis of cDNA, transfection of host cells,and in-vitro transcription. The variants can then be screened forfunctional activity.

More particularly, specific regions of the nucleic acid sequencesdisclosed herein, and the polypeptides they encode, may be used toidentify polymorphic variants, interspecies homologs, and alleles of thesequences. This identification can be made in vitro, e.g., understringent hybridization conditions, PCR, and sequencing, or by using thesequence information in a computer system for comparison with othernucleic acid sequences. Different alleles of T2R genes within a singlespecies population will also be useful in determining whetherdifferences in allelic sequences correlate to differences in tasteperception between members of the population.

The nucleic acid molecules of the present invention are generallyintronless and encode putative T2R proteins generally having lengths ofapproximately 300 residues and are comprised of seven transmembraneregions, as predicted by hydrophobicity plotting analysis, suggestingthat they belong to the G Protein-Coupled Receptor (7TM) superfamily. Inaddition to the overall structural similarity, each of the T2Rsidentified herein has a characteristic sequence signature of a T2Rfamily member. In particular, all sequences contain very close matchesto the T2R family consensus sequences identified above. Combination ofall the above mentioned structural features of the identified genes andencoded proteins strongly suggests that they represent novel members ofthe T2R receptor family.

It is also hypothesized that that T2R receptors and their genes can beused, alone or in combination with other types of taste receptors, indeveloping detection systems and assays for chemically identifyingdistinct types of molecules specifically recognized by these receptors,as well as for diagnostic and research purposes.

The nucleic acid sequences of the invention and other nucleic acids usedto practice this invention, whether RNA, cDNA, genomic DNA, vectors,viruses or hybrids thereof, may be isolated from a variety of sources,genetically engineered, amplified, and/or expressed recombinantly. Anyrecombinant expression system can be used, including, in addition tomammalian cells, e.g., bacterial, yeast, insect, or plant systems.

A. Identification of T2Rs

The amino acid sequences of the T2R proteins and polypeptides of theinvention can be identified by putative translation of the codingnucleic acid sequences. These various amino acid sequences and thecoding nucleic acid sequences may be compared to one another or to othersequences according to a number of methods. In a particular embodiment,the pseudogenes disclosed herein can be used to identify functionalalleles or related genes in genomic databases known in the art.

For example, in sequence comparison, typically one sequence acts as areference sequence, to which test sequences are compared. When using asequence comparison algorithm, test and reference sequences are enteredinto a computer, subsequence coordinates are designated, if necessary,and sequence algorithm program parameters are designated. Defaultprogram parameters can be used, as described below for the BLASTN andBLASTP programs, or alternative parameters can be designated. Thesequence comparison algorithm then calculates the percent sequenceidentities for the test sequences relative to the reference sequence,based on the program parameters.

A “comparison window,” as used herein, includes reference to a segmentof any one of the number of contiguous positions selected from the groupconsisting of from 20 to 600, usually about 50 to about 200, moreusually about 100 to about 150 in which a sequence may be compared to areference sequence of the same number of contiguous positions after thetwo sequences are optimally aligned. Methods of alignment of sequencesfor comparison are well known in the art. Optimal alignment of sequencesfor comparison can be conducted, e.g., by the local homology algorithmof Smith & Waterman, Adv. Appl. Math., 2:482 (1981), by the homologyalignment algorithm of Needleman & Wunsch, J. Mol. Biol. 48:443 (1970),by the search for similarity method of Pearson & Lipman, PNAS, 85:2444(1988), by computerized implementations of these algorithms (GAP,BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package,Genetics Computer Group, 575 Science Dr., Madison, Wis.), or by manualalignment and visual inspection (see, e.g., Current Protocols inMolecular Biology (Ausubel et al., eds. 1995 supplement)).

A preferred example of an algorithm that is suitable for determiningpercent sequence identity and sequence similarity are the BLAST andBLAST 2.0 algorithms, which are described in Altschul et al., Nuc. AcidsRes., 25:3389-402 (1977) and Altschul et al., J. Mol. Biol., 215:403-10(1990), respectively. Software for performing BLAST analyses is publiclyavailable through the National Center for Biotechnology Information(http://www.ncbi.nlm.nih.gov/). This algorithm involves firstidentifying high scoring sequence pairs (HSPs) by identifying shortwords of length W in the query sequence, which either match or satisfysome positive valued threshold score T when aligned with a word of thesame length in a database sequence. T is referred to as the neighborhoodword score threshold (Altschul et al., Altschul et al., Nuc. Acids Res.,25:3389-402 (1977) and Altschul et al., J Mol. Biol., 215:403-10(1990)). These initial neighborhood word hits act as seeds forinitiating searches to find longer HSPs containing them. The word hitsare extended in both directions along each sequence for as far as thecumulative alignment score can be increased. Cumulative scores arecalculated using, for nucleotide sequences, the parameters M (rewardscore for a pair of matching residues; always >0) and N (penalty scorefor mismatching residues; always <0). For amino acid sequences, ascoring matrix is used to calculate the cumulative score. Extension ofthe word hits in each direction are halted when: the cumulativealignment score falls off by the quantity X from its maximum achievedvalue; the cumulative score goes to zero or below, due to theaccumulation of one or more negative scoring residue alignments; or theend of either sequence is reached. The BLAST algorithm parameters W, T,and X determine the sensitivity and speed of the alignment. The BLASTNprogram (for nucleotide sequences) uses as defaults a wordlength (W) of11, an expectation (E) or 10, M=5, N=−4 and a comparison of bothstrands. For amino acid sequences, the BLASTP program uses as defaults awordlength of 3, and expectation (E) of 10, and the BLOSUM62 scoringmatrix (see Henikoff & Henikoff, PNAS, 89:10915 (1989)) alignments (B)of 50, expectation (E) of 10, M=5, N=−4, and a comparison of bothstrands.

Another example of a useful algorithm is PILEUP. PILEUP creates amultiple sequence alignment from a group of related sequences usingprogressive, pairwise alignments to show relationship and percentsequence identity. It also plots a so-called “tree” or “dendogram”showing the clustering relationships used to create the alignment.PILEUP uses a simplification of the progressive alignment method of Feng& Doolittle, J Mol. Evol., 35:351-60 (1987). The method used is similarto the method described by Higgins & Sharp, CABIOS 5:151-53 (1989). Theprogram can align up to 300 sequences, each of a maximum length of 5,000nucleotides or amino acids. The multiple alignment procedure begins withthe pairwise alignment of the two most similar sequences, producing acluster of two aligned sequences. This cluster is then aligned to thenext most related sequence or cluster of aligned sequences. Two clustersof sequences are aligned by a simple extension of the pairwise alignmentof two individual sequences. The final alignment is achieved by a seriesof progressive, pairwise alignments. The program is run by designatingspecific sequences and their amino acid or nucleotide coordinates forregions of sequence comparison and by designating the programparameters. Using PILEUP, a reference sequence is compared to other testsequences to determine the percent sequence identity relationship usingthe following parameters: default gap weight (3.00), default gap lengthweight (0.10), and weighted end gaps. PILEUP can be obtained from theGCG sequence analysis software package, e.g., version 7.0 Devereaux etal., Nuc. Acids Res., 12:387-95 (1984). Comparison of these proteinsequences to all known proteins in the public sequence databases usingBLASTP algorithm revealed their strong homology to the members of theT2R family, each of the T2R family sequences having at least 50%, andpreferably at least 55%, at least 60%, at least 65%, and most preferablyat least 70%, amino acid identity to at least one known member of thefamily.

B. Definitions

As used herein, the following terms have the meanings ascribed to themunless specified otherwise.

“Taste cells” include neuroepithelial cells that are organized intogroups to form taste buds of the tongue, e.g., foliate, fungiform, andcircumvallate cells (see, e.g., Roper et al., Ann. Rev. Neurosci.12:329-353 (1989)). Taste cells are also found in the palate, and othertissues such as the esophagus and the stomach.

“T2R” refers to one or more members of a family of G Protein-CoupledReceptors that are selectively expressed in taste cells of the tongueand palate epithelium, such as foliate, geschmackstreifen, epiglottis,fungiform, and circumvallate cells, as well as cells of the esophagus,and stomach (see, e.g., Adler et al., Cell, 100:693-702 (2000)). Thisfamily is also referred to as the “SF family” (see, e.g.,PCT/US00/24821, which is herein incorporated by reference in itsentirety). Such taste cells can be identified because they expressspecific molecules such as gustducin, a taste-cell-specific G Protein,or other taste specific molecules (McLaughin et al., Nature, 357:563-69(1992)). Taste receptor cells can also be identified on the basis ofmorphology (see, e.g., Roper, supra). T2R family members have theability to act as receptors for taste transduction. T2R family membersare also referred to as the “GR” family, for gustatory receptor, or “SF”family.

“T2R” nucleic acids encode a family of GPCRs with seven transmembraneregions that have “G Protein-Coupled Receptor activity,” e.g., they maybind to G Proteins in response to extracellular stimuli and promoteproduction of second messengers such as IP3, cAMP, cGMP, and Ca²⁺ viastimulation of enzymes such as phospholipase C and adenylate cyclase(for a description of the structure and function of GPCRs, see, e.g.,Fong, supra, and Baldwin, supra). These nucleic acids encode proteinsthat are expressed in taste cells, in particular gustducin-expressingtaste cells that are responsive to bitter tastants. A single taste cellmay contain many distinct T2R polypeptides.

The term “T2R” family therefore includes polymorphic variants, alleles,mutants, and homologs that: (1) have about 30-40% amino acid sequenceidentity, more specifically about 40, 50, 60, 70, 75, 80, 85, 90, 95,96, 97, 98, or 99% amino acid sequence identity to SEQ ID NOS: 2, 4, 6,8, 10, 12, 14, 16, 18, 20, and 24, over a window of about 25 aminoacids, optionally 50-100 amino acids; (2) specifically bind toantibodies raised against an immunogen comprising an amino acid sequenceselected from the group consisting of SEQ ID NOS: 2, 4, 6, 8, 10, 12,14, 16, 18, 20, and 24, and conservatively modified variants thereof;(3) specifically hybridize (with a size of at least about 100,optionally at least about 500-1000 nucleotides) under stringenthybridization conditions to a sequence selected from the groupconsisting of SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 23, andconservatively modified variants thereof; (4) comprise a sequence atleast about 40% identical to an amino acid sequence selected from thegroup consisting of SEQ ID NOS: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, and24; or (5) are amplified by primers that specifically hybridize understringent hybridization conditions to the same sequence as a degenerateprimer sets encoding SEQ ID NOS: 25-30.

As previously discussed, while T2R genes exhibit substantial sequencedivergence at both the protein and DNA level, all isolated to date havebeen found to contain comprise certain consensus sequences, inparticular regions that are identical or which possess or at least70-75% sequence identity to the T2R consensus sequence identifiedpreviously (SEQ ID NOS: 25-30).

Topologically, certain chemosensory GPCRs have an “N-terminal domain;”“extracellular domains,” a “transmembrane domain” comprising seventransmembrane regions, and corresponding cytoplasmic and extracellularloops, “cytoplasmic regions,” and a “C-terminal region” (see, e.g., Hoonet al., Cell, 96:541-51 (1999); Buck & Axel, Cell, 65:175-87 (1991)).These regions can be structurally identified using methods known tothose of skill in the art, such as sequence analysis programs thatidentify hydrophobic and hydrophilic domains (see, e.g., Stryer,Biochemistry, (3rd ed. 1988); see also any of a number of Internet basedsequence analysis programs, such as those found atdot.imgen.bcm.tmc.edu). These regions are useful for making chimericproteins and for in vitro assays of the invention, e.g., ligand bindingassays.

“Extracellular domains” therefore refers to the domains of T2Rpolypeptides that protrude from the cellular membrane and are exposed tothe extracellular face of the cell. Such regions would include the“N-terminal domain” that is exposed to the extracellular face of thecell, as well as the extracellular loops of the transmembrane domainthat are exposed to the extracellular face of the cell, i.e., theextracellular loops between transmembrane regions 2 and 3, transmembraneregions 4 and 5, and transmembrane regions 6 and 7. The “N-terminaldomain” starts at the N-terminus and extends to a region close to thestart of the transmembrane region. These extracellular regions areuseful for in vitro ligand binding assays, both soluble and solid phase.In addition, transmembrane regions, described below, can also beinvolved in ligand binding, either in combination with the extracellularregion or alone, and are therefore also useful for in vitro ligandbinding assays.

“Transmembrane domain,” which comprises the seven transmembrane“regions,” refers to the domain of T2R polypeptides that lies within theplasma membrane, and may also include the corresponding cytoplasmic(intracellular) and extracellular loops, also referred to astransmembrane “regions.” The seven transmembrane regions andextracellular and cytoplasmic loops can be identified using standardmethods, as described in Kyte & Doolittle, J. Mol. Biol., 157:105-32(1982)), or in Stryer, supra.

“Cytoplasmic domains” refers to the domains of T2R proteins that facethe inside of the cell, e.g., the “C-terminal domain” and theintracellular loops of the transmembrane domain, e.g., the intracellularloops between transmembrane regions 1 and 2, transmembrane regions 3 and4, and transmembrane regions 5 and 6. “C-terminal domain” refers to theregion that spans from the end of the last transmembrane region to theC-terminus of the protein, and which is normally located within thecytoplasm.

The term “7-transmembrane receptor” means a polypeptide belonging to asuperfamily of transmembrane proteins that have seven regions that spanthe plasma membrane seven times (thus, the seven regions are called“transmembrane” or “TM” domains TM I to TM VII). The families ofolfactory and certain taste receptors each belong to this super-family.7-transmembrane receptor polypeptides have similar and characteristicprimary, secondary and tertiary structures, as discussed in furtherdetail below.

The term “ligand-binding region” refers to sequences derived from achemosensory or taste receptor that substantially incorporatestransmembrane domains II to VII (TM II to VII). The region may becapable of binding a ligand, and more particularly, a tastant.

The term “plasma membrane translocation domain” or simply “translocationdomain” means a polypeptide domain that is functionally equivalent to anexemplary translocation domain (5′-MNGTEGPNFYVPFSNKTGVV; SEQ ID NO: 31).These peptide domains, when incorporated into the amino terminus of apolypeptide coding sequence, can with great efficiency “chaperone” or“translocate” the hybrid (“fusion”) protein to the cell plasma membrane.This particular “translocation domain” was initially derived from theamino terminus of the human rhodopsin receptor polypeptide, a7-transmembrane receptor. Another translocation domain has been derivedfrom the bovine rhodopsin sequence and is also useful for facilitatingtranslocation. Rhodopsin derived sequences are particularly efficient intranslocating 7-transmembrane fusion proteins to the plasma membrane.

“Functional equivalency” means the domain's ability and efficiency intranslocating newly translated proteins to the plasma membrane asefficiently as exemplary SEQ ID NO: 31 under similar conditions;relatively efficiencies an be measured (in quantitative terms) andcorn-pared, as described herein. Domains falling within the scope of theinvention can be determined by routine screening for their efficiency intranslocating newly synthesized polypeptides to the plasma membrane in acell (mammalian, Xenopus, and the like) with the same efficiency as thetwenty amino acid long translocation domain SEQ ID NO: 31.

The phrase “functional effects” in the context of assays for testingcompounds that modulate T2R family member mediated taste transductionincludes the determination of any parameter that is indirectly ordirectly under the influence of the receptor, e.g., functional, physicaland chemical effects. It includes ligand binding, changes in ion flux,membrane potential, current flow, transcription, G Protein binding, GPCRphosphorylation or dephosphorylation, signal transduction,receptor-ligand interactions, second messenger concentrations (e.g.,cAMP, cGMP, IP3, or intracellular Ca²⁺), in vitro, in vivo, and ex vivoand also includes other physiologic effects such increases or decreasesof neurotransmitter or hormone release.

By “determining the functional effect” is meant assays for a compoundthat increases or decreases a parameter that is indirectly or directlyunder the influence of a T2R family member, e.g., functional, physicaland chemical effects. Such functional effects can be measured by anymeans known to those skilled in the art, e.g., changes in spectroscopiccharacteristics (e.g., fluorescence, absorbance, refractive index),hydrodynamic (e.g., shape), chromatographic, or solubility properties,patch clamping, voltage-sensitive dyes, whole cell currents,radioisotope efflux, inducible markers, oocyte T2R gene expression;tissue culture cell T2R expression; transcriptional activation of T2Rgenes; ligand binding assays; voltage, membrane potential andconductance changes; ion flux assays; changes in intracellular secondmessengers such as cAMP, cGMP, and inositol triphosphate (IP3); changesin intracellular calcium levels; neurotransmitter release, and the like.

“Inhibitors,” “activators,” and “modulators” of T2R genes or proteinsare used interchangeably to refer to inhibitory, activating, ormodulating molecules identified using in vitro and in vivo assays fortaste transduction, e.g., ligands, agonists, antagonists, and theirhomologs and mimetics. Inhibitors are compounds that, e.g., bind to,partially or totally block stimulation, decrease, prevent, delayactivation, inactivate, desensitize, or down regulate tastetransduction, e.g., antagonists. Activators are compounds that, e.g.,bind to, stimulate, increase, open, activate, facilitate, enhanceactivation, sensitize, or up regulate taste transduction, e.g.,agonists. Modulators include compounds that, e.g., alter the interactionof a receptor with: extracellular proteins that bind activators orinhibitor (e.g., ebnerin and other members of the hydrophobic carrierfamily); G Proteins; kinases (e.g., homologs of rhodopsin kinase andbeta adrenergic receptor kinases that are involved in deactivation anddesensitization of a receptor); and arrestins, which also deactivate anddesensitize receptors. Modulators include genetically modified versionsof T2R family members, e.g., with altered activity, as well as naturallyoccurring and synthetic ligands, antagonists, agonists, small chemicalmolecules and the like.

Such assays for inhibitors and activators include, e.g., expressing T2Rfamily members in cells or cell membranes, applying putative modulatorcompounds in the presence or absence of tastants, e.g., bitter tastants,and then determining the functional effects on taste transduction, asdescribed above. Samples or assays comprising T2R family members thatare treated with a potential activator, inhibitor, or modulator arecompared to control samples without the inhibitor, activator, ormodulator to examine the extent of modulation. Control samples(untreated with modulators) are assigned a relative T2R activity, valueof 100%. Inhibition of a T2R is achieved when the T2R activity valuerelative to the control is about 80%, optionally 50% or 25-0%.Activation of a T2R is achieved when the T2R activity value relative tothe control is 110%, optionally 150%, optionally 200-500%, or 1000-3000%higher.

The terms “purified,” “substantially purified,” and “isolated” as usedherein refer to the state of being free of other, dissimilar compoundswith which the compound of the invention is normally associated in itsnatural state. Preferably, “purified,” “substantially purified,” and“isolated” means that the composition comprises at least 0.5%, 1%, 5%,10%, or 20%, and most preferably at least 50% or 75% of the mass, byweight, of a given sample. In one preferred embodiment, these termsrefer to the compound of the invention comprising at least 95% of themass, by weight, of a given sample. As used herein, the terms“purified,” “substantially purified,” and “isolated” “isolated,” whenreferring to a nucleic acid or protein, of nucleic acids or proteins,also refers to a state of purification or concentration different thanthat which occurs naturally in the mammalian, especially human, body.Any degree of purification or concentration greater than that whichoccurs naturally in the mammalian, especially human, body, including (1)the purification from other associated structures or compounds or (2)the association with structures or compounds to which it is not normallyassociated in the mammalian, especially human, body, are within themeaning of “isolated.” The nucleic acid or protein or classes of nucleicacids or proteins, described herein, may be isolated, or otherwiseassociated with structures or compounds to which they are not normallyassociated in nature, according to a variety of methods and processesknown to those of skill in the art.

As used herein, the term “isolated,” when referring to a nucleic acid orpolypeptide refers to a state of purification or concentration differentthan that which occurs naturally in the mammalian, especially human,body. Any degree of purification or concentration greater than thatwhich occurs naturally in the body, including (1) the purification fromother naturally-occurring associated structures or compounds, or (2) theassociation with structures or compounds to which it is not normallyassociated in the body are within the meaning of “isolated” as usedherein. The nucleic acids or polypeptides described herein may beisolated or otherwise associated with structures or compounds to whichthey are not normally associated in nature, according to a variety ofmethods and processed known to those of skill in the art.

As used herein, the terms “amplifying” and “amplification” refer to theuse of any suitable amplification methodology for generating ordetecting recombinant or naturally expressed nucleic acid, as describedin detail, below. For example, the invention provides methods andreagents (e.g., specific oligonucleotide primer pairs) for amplifying(e.g., by polymerase chain reaction, PCR) naturally expressed (e.g.,genomic or mRNA) or recombinant (e.g., cDNA) nucleic acids of theinvention (e.g., tastant-binding sequences of the invention) in vivo orin vitro.

The term “expression vector” refers to any recombinant expression systemfor the purpose of expressing a nucleic acid sequence of the inventionin vitro or in vivo, constitutively or inducibly, in any cell, includingprokaryotic, yeast, fungal, plant, insect or mammalian cell. The termincludes linear or circular expression systems. The term includesexpression systems that remain episomal or integrate into the host cellgenome. The expression systems can have the ability to self-replicate ornot, i.e., drive only transient expression in a cell. The term includesrecombinant expression “cassettes which contain only the minimumelements needed for transcription of the recombinant nucleic acid.

The term “library” means a preparation that is a mixture of differentnucleic acid or poly-peptide molecules, such as the library ofrecombinantly generated sensory, particularly taste receptorligand-binding regions generated by amplification of nucleic acid withdegenerate primer pairs, or an isolated collection of vectors thatincorporate the amplified ligand-binding regions, or a mixture of cellseach randomly transfected with at least one vector encoding an tastereceptor.

The term “nucleic acid” or “nucleic acid sequence” refers to adeoxy-ribonucleotide or ribonucleotide oligonucleotide in either single-or double-stranded form. The term encompasses nucleic acids, i.e.,oligonucleotides, containing known analogs of natural nucleotides. Theterm also encompasses nucleic-acid-like structures with syntheticbackbones.

Unless otherwise indicated, a particular nucleic acid sequence alsoimplicitly encompasses conservatively modified variants thereof (e.g.,degenerate codon substitutions) and complementary sequences, as well asthe sequence explicitly indicated. Specifically, degenerate codonsubstitutions may be achieved by generating, e.g., sequences in whichthe third position of one or more selected codons is substituted withmixed-base and/or deoxyinosine residues (Batzer et al., Nucleic AcidRes., 19:5081 (1991); Ohtsuka et al., J. Biol. Chem., 260:2605-08(1985); Rossolini et al., Mol. Cell. Probes, 8:91-98 (1994)). The termnucleic acid is used interchangeably with gene, cDNA, mRNA,oligonucleotide, and polynucleotide.

The terms “polypeptide,” “peptide” and “protein” are usedinterchangeably herein to refer to a polymer of amino acid residues. Theterms apply to amino acid polymers in which one or more amino acidresidue is an artificial chemical mimetic of a corresponding naturallyoccurring amino acid, as well as to naturally occurring amino acidpolymers and non-naturally occurring amino acid polymer.

The “translocation domain,” “ligand-binding region”, and chimericreceptors compositions described herein also include “analogs,” or“conservative variants” and “mimetics” (“peptidomimetics”) withstructures and activity that substantially correspond to the exemplarysequences. Thus, the terms “conservative variant” or “analog” or“mimetic” refer to a polypeptide which has a modified amino acidsequence, such that the change(s) do not substantially alter thepolypeptide's (the conservative variant's) structure and/or activity, asdefined herein. These include conservatively modified variations of anamino acid sequence, i.e., amino acid substitutions, additions ordeletions of those residues that are not critical for protein activity,or substitution of amino acids with residues having similar properties(e.g., acidic, basic, positively or negatively charged, polar ornon-polar, etc.) such that the substitutions of even critical aminoacids does not substantially alter structure and/or activity.

More particularly, “conservatively modified variants” applies to bothamino acid and nucleic acid sequences. With respect to particularnucleic acid sequences, conservatively modified variants refers to thosenucleic acids which encode identical or essentially identical amino acidsequences, or where the nucleic acid does not encode an amino acidsequence, to essentially identical sequences. Because of the degeneracyof the genetic code, a large number of functionally identical nucleicacids encode any given protein.

For instance, the codons GCA, GCC, GCG and GCU all encode the amino acidalanine. Thus, at every position where an alanine is specified by acodon, the codon can be altered to any of the corresponding codonsdescribed without altering the encoded polypeptide.

Such nucleic acid variations are “silent variations,” which are onespecies of conservatively modified variations. Every nucleic acidsequence herein which encodes a polypeptide also describes everypossible silent variation of the nucleic acid. One of skill willrecognize that each codon in a nucleic acid (except AUG, which isordinarily the only codon for methionine, and TGG, which is ordinarilythe only codon for tryptophan) can be modified to yield a functionallyidentical molecule. Accordingly, each silent variation of a nucleic acidwhich encodes a polypeptide is implicit in each described sequence.

Conservative substitution tables providing functionally similar aminoacids are well known in the art. For example, one exemplary guideline toselect conservative substitutions includes (original residue followed byexemplary substitution): ala/gly or ser; arg/lys; asn/gln or his;asp/glu; cys/ser; gln/asn; gly/asp; gly/ala or pro; his/asn or gln;ile/leu or val; leu/ile or val; lys/arg or gln or glu; met/leu or tyr orile; phe/met or leu or tyr; ser/thr; thr/ser; trp/tyr; tyr/trp or phe;val/ile or leu. An alternative exemplary guideline uses the followingsix groups, each containing amino acids that are conservativesubstitutions for one another: 1) Alanine (A), Serine (S), Threonine(T); 2) Aspartic acid (D), Glutamic acid (E); 3) Asparagine (N),Glutamine (Q); 4) Arginine (R), Lysine (I); 5) Isoleucine (I), Leucine(L), Methionine (M), Valine (V); and 6) Phenylalanine (F), Tyrosine (Y),Tryptophan (W); (see also, e.g., Creighton, Proteins, W.H. Freeman andCompany (1984); Schultz and Schimer, Principles of Protein Structure,Springer-Verlag (1979)). One of skill in the art will appreciate thatthe above-identified substitutions are not the only possibleconservative substitutions. For example, for some purposes, one mayregard all charged amino acids as conservative substitutions for eachother whether they are positive or negative. In addition, individualsubstitutions, deletions or additions that alter, add or delete a singleamino acid or a small percentage of amino acids in an encoded sequencecan also be considered “conservatively modified variations.”

The terms “mimetic” and “peptidomimetic” refer to a synthetic chemicalcompound that has substantially the same structural and/or functionalcharacteristics of the polypeptides, e.g., translocation domains,ligand-binding regions, or chimeric receptors of the invention. Themimetic can be either entirely composed of synthetic, non-naturalanalogs of amino acids, or may be a chimeric molecule of partly naturalpeptide amino acids and partly non-natural analogs of amino acids. Themimetic can also incorporate any amount of natural amino acidconservative substitutions as long as such substitutions also do notsubstantially alter the mimetic's structure and/or activity.

As with polypeptides of the invention which are conservative variants,routine experimentation will determine whether a mimetic is within thescope of the invention, i.e., that its structure and/or function is notsubstantially altered. Polypeptide mimetic compositions can contain anycombination of non-natural structural components, which are typicallyfrom three structural groups: a) residue linkage groups other than thenatural amide bond (“peptide bond”) linkages; b) non-natural residues inplace of naturally occurring amino acid residues; or c) residues whichinduce secondary structural mimicry, i.e., to induce or stabilize asecondary structure, e.g., a beta turn, gamma turn, beta sheet, alphahelix conformation, and the like. A polypeptide can be characterized asa mimetic when all or some of its residues are joined by chemical meansother than natural peptide bonds. Individual peptidomimetic residues canbe joined by peptide bonds, other chemical bonds or coupling means, suchas, e.g., glutaraldehyde, N-hydroxysuccinimide esters, bifunctionalmaleimides, N,N′-dicyclohexylcarbodiimide (DCC) orN,N′-diisopropylcarbodiimide (DIC). Linking groups that can be analternative to the traditional amide bond (“peptide bond”) linkagesinclude, e.g., ketomethylene (e.g., —C(═O)—CH₂— for —C(═O)—NH—),aminomethylene (CH₂—NH), ethylene, olefin (CH═CH), ether (CH₂—O),thioether (CH₂—S), tetrazole (CN₄), thiazole, retroamide, thioamide, orester (see, e.g., Spatola, Chemistry and Biochemistry of Amino Acids,Peptides and Proteins, Vol. 7, 267-357, Marcell Dekker, Peptide BackboneModifications, NY (1983)). A polypeptide can also be characterized as amimetic by containing all or some non-natural residues in place ofnaturally occurring amino acid residues; non-natural residues are welldescribed in the scientific and patent literature.

A “label” or a “detectable moiety” is a composition detectable byspectroscopic, photochemical, biochemical, immunochemical, or chemicalmeans. For example, useful labels include ³²P, fluorescent dyes,electron-dense reagents, enzymes (e.g., as commonly used in an ELISA),biotin, digoxigenin, or haptens and proteins which can be madedetectable, e.g., by incorporating a radiolabel into the peptide or usedto detect antibodies specifically reactive with the peptide.

A “labeled nucleic acid probe or oligonucleotide” is one that is bound,either covalently, through a linker or a chemical bond, ornoncovalently, through ionic; van der Waals, electrostatic, or hydrogenbonds to a label such that the presence of the probe may be detected bydetecting the presence of the label bound to the probe.

As used herein a “nucleic acid probe or oligonucleotide” is defined as anucleic acid capable of binding to a target nucleic acid ofcomplementary sequence through one or more types of chemical bonds,usually through complementary base pairing, usually through hydrogenbond formation. As used herein, a probe may include natural (i.e., A, G,C, or T) or modified bases (7-deazaguanosine, inosine, etc.). Inaddition, the bases in a probe may be joined by a linkage other than aphosphodiester bond, so long as it does not interfere withhybridization. Thus, for example, probes may be peptide nucleic acids inwhich the constituent bases are joined by peptide bonds rather thanphosphodiester linkages. It will be understood by one of skill in theart that probes may bind target sequences lacking completecomplementarity with the probe sequence depending upon the stringency ofthe hybridization conditions. The probes are optionally directly labeledas with isotopes, chromophores, lumiphores, chromogens, or indirectlylabeled such as with biotin to which a streptavidin complex may laterbind. By assaying for the presence or absence of the probe, one candetect the presence or absence of the select sequence or subsequence.

The term “heterologous” when used with reference to portions of anucleic acid indicates that the nucleic acid comprises two or moresubsequences that are not found in the same relationship to each otherin nature. For instance, the nucleic acid is typically recombinantlyproduced, having two or more sequences from unrelated genes arranged tomake a new functional nucleic acid, e.g., a promoter from one source anda coding region from another source. Similarly, a heterologous proteinindicates that the protein comprises two or more subsequences that arenot found in the same relationship to each other in nature (e.g., afusion protein).

A “promoter” is defined as an array of nucleic acid sequences thatdirect transcription of a nucleic acid. As used herein, a promoterincludes necessary nucleic acid sequences near the start site oftranscription, such as, in the case of a polymerase II type promoter, aTATA element. A promoter also optionally includes distal enhancer orrepressor elements, which can be located as much as several thousandbase pairs from the start site of transcription. A “constitutive”promoter is a promoter that is active under most environmental anddevelopmental conditions. An “inducible” promoter is a promoter that isactive under environmental or developmental regulation. The term“operably linked” refers to a functional linkage between a nucleic acidexpression control sequence (such as a promoter; or array oftranscription factor binding sites) and a second nucleic acid sequence,wherein the expression control sequence directs transcription of thenucleic acid corresponding to the second sequence.

As used herein, “recombinant” refers to a polynucleotide synthesized orotherwise manipulated in vitro (e.g., “recombinant polynucleotide”), tomethods of using recombinant polynucleotides to produce gene products incells or other biological systems, or to a polypeptide (“recombinantprotein”) encoded by a recombinant polynucleotide. “Recombinant means”also encompass the ligation of nucleic acids having various codingregions or domains or promoter sequences from different sources into anexpression cassette or vector for expression of, e.g., inducible orconstitutive expression of a fusion protein comprising a translocationdomain of the invention and a nucleic acid sequence amplified using aprimer of the invention.

The phrase “selectively (or specifically) hybridizes to” refers to thebinding, duplexing, or hybridizing of a molecule only to a particularnucleotide sequence under stringent hybridization conditions when thatsequence is present in a complex mixture (e.g., total cellular orlibrary DNA or RNA).

The phrase “stringent hybridization conditions” refers to conditionsunder which a probe will hybridize to its target subsequence, typicallyin a complex mixture of nucleic acid, but to no other sequences.Stringent conditions are sequence dependent and will be different indifferent circumstances. Longer sequences hybridize specifically athigher temperatures. An extensive guide to the hybridization of nucleicacids is found in Tijssen, Techniques in Biochemistry and MolecularBiology—Hybridisation with Nucleic Probes, “Overview of principles ofhybridization and the strategy of nucleic acid assays” (1993).Generally, stringent conditions are selected to be about 5-10° C. lowerthan the thermal melting point (Tm) for the specific sequence at adefined ionic strength pH. The Tm is the temperature (under definedionic strength, pH, and nucleic concentration) at which 50% of theprobes complementary to the target hybridize to the target sequence atequilibrium (as the target sequences are present in excess, at Tm, 50%of the probes are occupied at equilibrium). Stringent conditions will bethose in which the salt concentration is less than about 1.0 M sodiumion, typically about 0.01 to 1.0 M sodium ion concentration (or othersalts) at pH 7.0 to 8.3 and the temperature is at least about 30° C. forshort probes (e.g., 10 to 50 nucleotides) and at least about 60° C. forlong probes (e.g., greater than 50 nucleotides). Stringent conditionsmay also be achieved with the addition of destabilizing agents such asformamide. For selective or specific hybridization, a positive signal isat least two times background, optionally 10 times backgroundhybridization. Exemplary stringent hybridization conditions can be asfollowing: 50% formamide, 5×SSC, and 1% SDS, incubating at 42° C., or,5×SSC, 1% SDS, incubating at 65° C., with wash in 0.2×SSC, and 0.1% SDSat 65° C. Such hybridizations and wash steps can be carried out for,e.g., 1, 2, 5, 10, 15, 30, 60; or more minutes.

Nucleic acids that do not hybridize to each other under stringentconditions are still substantially related if the polypeptides whichthey encode are substantially related. This occurs, for example, when acopy of a nucleic acid is created using the maximum codon degeneracypermitted by the genetic code. In such cases, the nucleic acidstypically hybridize under moderately stringent hybridization conditions.Exemplary “moderately stringent hybridization conditions” include ahybridization in a buffer of 40% formamide, 1 M NaCl, 1% SDS at 37° C.,and a wash in 1×SSC at 45° C. Such hybridizations and wash steps can becarried out for, e.g., 1, 2, 5, 10, 15, 30, 60, or more minutes. Apositive hybridization is at least twice background. Those of ordinaryskill will readily recognize that alternative hybridization and washconditions can be utilized to provide conditions of similar stringency.

“Antibody” refers to a polypeptide comprising a framework region from animmunoglobulin gene or fragments thereof that specifically binds andrecognizes an antigen. The recognized immunoglobulin genes include thekappa, lambda, alpha, gamma, delta, epsilon, and mu constant regiongenes, as well as the myriad immunoglobulin variable region genes. Lightchains are classified as either kappa or lambda. Heavy chains areclassified as gamma, mu, alpha, delta, or epsilon, which in turn definethe immunoglobulin classes, IgG, IgM, IgA, IgD and IgE, respectively.

An exemplary immunoglobulin (antibody) structural unit comprises atetramer. Each tetramer is composed of two identical pairs ofpolypeptide chains, each pair having one “light” (about 25 kDa) and one“heavy” chain (about 50-70 kDa). The N-terminus of each chain defines avariable region of about 100 to 110 or more amino acids primarilyresponsible for antigen recognition. The terms variable light chain (VL)and variable heavy chain (VH) refer to these light and heavy chainsrespectively.

A “chimeric antibody” is an antibody molecule in which (a) the constantregion, or a portion thereof, is altered, replaced or exchanged so thatthe antigen binding site (variable region) is linked to a constantregion of a different or altered class, effector function and/orspecies, or an entirely different molecule which confers new propertiesto the chimeric antibody, e.g., an enzyme, toxin, hormone, growthfactor, drug, etc.; or (b) the variable region, or a portion thereof, isaltered, replaced or exchanged with a variable region having a differentor altered antigen specificity.

An “anti-T2R” antibody is an antibody or antibody fragment thatspecifically binds a polypeptide encoded by a T2R gene, cDNA, or asubsequence thereof.

The term “immunoassay” is an assay that uses an antibody to specificallybind an antigen. The immunoassay is characterized by the use of specificbinding properties of a particular antibody to isolate, target, and/orquantify the antigen.

The phrase “specifically (or selectively) binds” to an antibody or,“specifically (or selectively) immunoreactive with,” when referring to aprotein or peptide, refers to a binding reaction that is determinativeof the presence of the protein in a heterogeneous population of proteinsand other biologics. Thus, under designated immunoassay conditions, thespecified antibodies bind to a particular protein at least two times thebackground and do not substantially bind in a significant amount toother proteins present in the sample. Specific binding to an antibodyunder such conditions may require an antibody that is selected for itsspecificity for a particular protein.

For example, polyclonal antibodies raised to a T2R family member fromspecific species such as rat, mouse, or human can be selected to obtainonly those polyclonal antibodies that are specifically immunoreactivewith the T2R polypeptide or an immunogenic portion thereof and not withother proteins, except for orthologs or polymorphic variants and allelesof the T2R polypeptide. This selection may be achieved by subtractingout antibodies that cross-react with T2R molecules from other species orother T2R molecules. Antibodies can also be selected that recognize onlyT2R GPCR family members but not GPCRs from other families. A variety ofimmunoassay formats may be used to select antibodies specificallyimmunoreactive with a particular protein. For example, solid-phase ELISAimmunoassays are routinely used to select antibodies specificallyimmunoreactive with a protein (see, e.g., Harlow & Lane, Antibodies, ALaboratory Manual, (1988), for a description of immunoassay formats andconditions that can be used to determine specific immunoreactivity).Typically a specific or selective reaction will be at least twicebackground signal or noise and more typically more than 10 to 100 timesbackground.

The phrase “selectively associates with” refers to the ability of anucleic acid to “selectively hybridize” with another as defined above,or the ability of an antibody to “selectively (or specifically) bind toa protein, as defined above.

The term “expression vector” refers to any recombinant expression systemfor the purpose of expressing a nucleic acid sequence of the inventionin vitro or in vivo, constitutively or inducibly, in any cell, includingprokaryotic, yeast, fungal, plant, insect or mammalian cell. The termincludes linear or circular expression systems. The term includesexpression systems that remain episomal or integrate into the host cellgenome. The expression systems can have the ability to self-replicate ornot, i.e., drive only transient expression in a cell. The term includesrecombinant expression “cassettes which contain only the minimumelements needed for transcription of the recombinant nucleic acid.

By “host cell” is meant a cell that contains an expression vector andsupports the replication or expression of the expression vector. Hostcells may be prokaryotic cells such as E. toll, or eukaryotic cells suchas yeast, insect, amphibian, or mammalian cells such as CHO, HeLa,HEK-293, and the like, e.g., cultured cells, explants, and cells invivo.

C. Isolation and Expression of T2Rs

Isolation and expression of the T2Rs, or fragments or variants thereof,of the invention can be effected by well established cloning proceduresusing probes or primers constructed based on the T2R nucleic acidssequences disclosed in the application. Related T2R sequences may alsobe identified from human or other species genomic databases using thesequences disclosed herein and known computer-based search technologies,e.g., BLAST sequence searching. In a particular embodiment, thepseudogenes disclosed herein can be used to identify functional allelesor related genes.

Expression vectors can then be used to infect or transfect host cellsfor the functional expression of these sequences. These genes andvectors can be made and expressed in vitro or in vivo. One of skill willrecognize that desired phenotypes for altering and controlling nucleicacid expression can be obtained by modulating the expression or activityof the genes and nucleic acids (e.g., promoters, enhancers and the like)within the vectors of the invention. Any of the known methods describedfor increasing or decreasing expression or activity can be used. Theinvention can be practiced in conjunction with any method or protocolknown in the art, which are well described in the scientific and patentliterature.

Alternatively, these nucleic acids can be synthesized in vitro bywell-known chemical synthesis techniques, as described in, e.g.,Carruthers, Cold Spring Harbor Symp. Quant. Biol. 47:411-18 (1982);Adams, Am. Chem. Soc., 105:661 (1983); Belousov, Nucleic Acids Res.25:3440-3444 (1997); Frenkel, Free Radic. Biol. Med. 19:373-380 (1995);Blommers, Biochemistry 33:7886-7896 (1994); Narang, Meth. Enzymol. 68:90(1979); Brown, Meth. Enzymol. 68:109 (1979); Beaucage, Tetra. Lett.22:1859 (1981); U.S. Pat. No. 4,458,066. Double-stranded DNA fragmentsmay then be obtained either by synthesizing the complementary strand andannealing the strands together under appropriate conditions, or byadding the complementary strand using DNA polymerase with an appropriateprimer sequence.

Techniques for the manipulation of nucleic acids, such as, for example,for generating mutations in sequences, subcloning, labeling probes,sequencing, hybridization and the like are well described in thescientific and patent literature. See, e.g., Sambrook, ed., MolecularCloning: A Laboratory Manual (2nd ed.), Vols. 1-3, Cold Spring HarborLaboratory (1989); Ausubel, ed., Current Protocols in Molecular Biology,John Wiley & Sons, Inc., New York (1997); Tijssen, ed., LaboratoryTechniques in Biochemistry and Molecular Biology: Hybridization WithNucleic Acid Probes, Part I, Theory and Nucleic Acid Preparation,Elsevier, N.Y. (1993).

Nucleic acids, vectors, capsids, polypeptides, and the like can beanalyzed and quantified by any of a number of general means well knownto those of skill in the art. These include, e.g., analyticalbiochemical methods such as NMR, spectrophotometry, radiography,electrophoresis, capillary electrophoresis, high performance liquidchromatography (HPLC), thin layer chromatography (TLC), andhyperdiffusion chromatography, various immunological methods, e.g.,fluid or gel precipitin reactions, immunodiffusion,immunoelectrophoresis, radioimmunoassays (RIAs), enzyme-linkedimmunosorbent assays (ELISAs), immuno-fluorescent assays, Southernanalysis, Northern analysis, dot-blot analysis, gel electrophoresis(e.g., SDS-PAGE), RT-PCR, quantitative PCR, other nucleic acid or targetor signal amplification methods, radiolabeling, scintillation counting,and affinity chromatography.

Oligonucleotide primers may be used to amplify nucleic acids encoding aT2R ligand-binding region. The nucleic acids described herein can alsobe cloned or measured quantitatively using amplification techniques.Amplification methods are also well known in the art, and include, e.g.,polymerase chain reaction (PCR) (Innis ed., PCR Protocols, a Guide toMethods and Applications, Academic Press, N.Y. (1990); Innis ed., PCRStrategies, Academic Press, Inc., N.Y. (1995)); ligase chain reaction(LCR) (Wu, Genomics, 4:560 (1989); Landegren, Science, 241:1077 (1988);Barringer, Gene, 89:117 (1990)); transcription amplification (Kwoh,PNAS, 86:1173 (1989)); self-sustained sequence replication (Guatelli,PNAS, 87:1874 (1990)); Q Beta replicase amplification (Smith, J. Clin.Microbiol., 35:1477-91 (1997)); automated Q-beta replicase amplificationassay (Burg, Mol. Cell. Probes, 10:257-71 (1996)); and other RNApolymerase mediated techniques (e.g., NASBA, Cangene, Mississauga,Ontario). See also, Berger, Methods Enzymol., 152:307-16 (1987);Sambrook; Ausubel; U.S. Pat. Nos. 4,683,195 and 4,683,202; Sooknanan,Biotechnology, 13:563-64 (1995).

Once amplified, the nucleic acids, either individually or as libraries,may be cloned according to methods known in the art, if desired, intoany of a variety of vectors using routine molecular biological methods;methods for cloning in vitro amplified nucleic acids are described,e.g., U.S. Pat. No. 5,426,039. To facilitate cloning of amplifiedsequences, restriction enzyme sites can be “built into” the PCR primerpair. For example, Pst I and Bsp E1 sites were designed into theexemplary primer pairs of the invention. These particular restrictionsites have a sequence that, when ligated, are “in-frame” with respect tothe 7-membrane receptor “donor” coding sequence into which they arespliced (the ligand-binding region coding sequence is internal to the7-membrane polypeptide, thus, if it is desired that the construct betranslated downstream of a restriction enzyme splice site, out of frameresults should be avoided; this may not be necessary if the insertedligand-binding region comprises substantially most of the transmembraneVII region). The primers can be designed to retain the original sequenceof the “donor” 7-membrane receptor. Alternatively, the primers canencode amino acid residues that are conservative substitutions (e.g.,hydrophobic for hydrophobic residue, see above discussion) orfunctionally benign substitutions (e.g., do not prevent plasma membraneinsertion, cause cleavage by peptidase, cause abnormal folding ofreceptor, and the like).

The primer pairs may be designed to selectively amplify ligand-bindingregions of T2R proteins. These binding regions may vary for differentligands; thus, what may be a minimal binding region for one ligand, maybe too limiting for a second potential ligand. Thus, binding regions ofdifferent sizes comprising different domain structures may be amplified;for example, transmembrane (TM) domains II through VII, III through VII,III through VI or II through VI, or variations thereof (e.g., only asubsequence of a particular domain, mixing the order of the domains, andthe like), of a 7-transmembrane T2R.

As domain structures and sequence of many 7-membrane T2R proteins areknown, the skilled artisan can readily select domain-flanking andinternal domain sequences as Model sequences to design degenerateamplification primer pairs. For example, a nucleic acid sequenceencoding domain regions H through VII can be generated by PCRamplification using a primer pair. To amplify a nucleic acid comprisingtransmembrane domain I (TM I) sequence, a degenerate primer can bedesigned from a nucleic acid that encodes the amino acid sequence of theT2R family consensus sequence 1 described above. Such a degenerateprimer can be used to generate a binding region incorporating TM Ithrough TM III, TM I through TM IV, TM I through TM V, TM I through TMVI or TM I through TM VII). Other degenerate primers can be designedbased on the other T2R family consensus sequences provided herein. Sucha degenerate primer can be used to generate a binding regionincorporating TM III through TM IV, TM III through TM V, TM III throughTM VI or TM III through TM VII.

Paradigms to design degenerate primer pairs are well known in the art.For example, a COnsensus-DEgenerate Hybrid Oligonucleotide Primer(CODEHOP) strategy computer program is accessible ashttp://blocks.fhcrc.org/codehop.html, and is directly linked from theBlockMaker multiple sequence alignment site for hybrid primer predictionbeginning with a set of related protein sequences, as known tastereceptor ligand-binding regions (see, e.g., Rose, Nucleic Acids Res.,26:1628-35 (1998); Singh, Biotechniques, 24:318-19 (1998)).

Means to synthesize oligonucleotide primer pairs are well known in theart. “Natural” base pairs or synthetic base pairs can be used. Forexample, use of artificial nucleobases offers a versatile approach tomanipulate primer sequence and generate a more complex mixture ofamplification products. Various families of artificial nucleobases arecapable of assuming multiple hydrogen bonding orientations throughinternal bond rotations to provide a means for degenerate molecularrecognition. Incorporation of these analogs into a single position of aPCR primer allows for generation of a complex library of amplificationproducts. See. e.g., Hoops, Nucleic Acids Res., 25:4866-71 (1997).Nonpolar molecules can also be used to mimic the shape of natural DNAbases. A non-hydrogen-bonding shape mimic for adenine can replicateefficiently and selectively against a nonpolar shape mimic for thymine(see, e.g., Morales, Nat. Struct. Biol., 5:950-54 (1998)). For example,two degenerate bases can be the pyrimidine base 6H,8H-3,4-dihydropyrimido[4,5-c][1,2]oxazin-7-one or the purine baseN6-methoxy-2,6-diaminopurine (see, e.g., Hill, PNAS, 95:4258-63 (1998)).Exemplary degenerate primers of the invention incorporate the nucleobaseanalog5′-Dimethoxytrityl-N-benzoyl-2′-deoxy-Cytidine,3′-[(2-cyanoethyl)-(N,N-diisopropyl)]-phosphoramidite(the term “P” in the sequences, see above). This pyrimidine analoghydrogen bonds with purines, including A and G residues.

Polymorphic variants, alleles, and interspecies homologs that aresubstantially identical to a taste receptor disclosed herein can beisolated using the nucleic acid probes described above. Alternatively,expression libraries can be used to clone T2R polypeptides andpolymorphic variants, alleles, and interspecies homologs thereof, bydetecting expressed homologs immunologically with antisera or purifiedantibodies made against a T2R polypeptide, which also recognize andselectively bind to the T2R homolog.

Nucleic acids that encode ligand-binding regions of taste receptors maybe generated by amplification (e.g., PCR) of appropriate nucleic acidsequences using appropriate (perfect or degenerate) primer pairs. Theamplified nucleic acid can be genomic DNA from any cell or tissue ormRNA or cDNA derived from taste receptor-expressing cells.

In one embodiment, hybrid protein-coding sequences comprising nucleicacids encoding T2Rs fused to a translocation sequences may beconstructed. Also provided are hybrid T2Rs comprising the translocationmotifs and tastant-binding regions of other families of chemosensoryreceptors, particularly taste receptors. These nucleic acid sequencescan be operably linked to transcriptional or translational controlelements, e.g., transcription and translation initiation sequences,promoters and enhancers, transcription and translation terminators,polyadenylation sequences, and other sequences useful for transcribingDNA into RNA. In construction of recombinant expression cassettes,vectors, and transgenics, a promoter fragment can be employed to directexpression of the desired nucleic acid in all desired cells or tissues.

In another embodiment, fusion proteins may include C-terminal orN-terminal translocation sequences. Further, fusion proteins cancomprise additional elements, e.g., for protein detection, purification,or other applications. Detection and purification facilitating domainsinclude, e.g., metal chelating peptides such as polyhistidine tracts,histidine-tryptophan modules, or other domains that allow purificationon immobilized metals; maltose binding protein; protein A domains thatallow purification on immobilized immunoglobulin; or the domain utilizedin the FLAGS extension/affinity purification system (Immunex Corp,Seattle Wash.).

The inclusion of a cleavable linker sequences such as Factor Xa (see,e.g., Ottavi, Biochimie, 80:289-93 (1998)), subtilisin proteaserecognition motif (see, e.g., Polyak, Protein Eng., 10:615-19 (1997));enterokinase (Invitrogen, San Diego, Calif.), and the like, between thetranslocation domain (for efficient plasma membrane expression) and therest of the newly translated polypeptide may be useful to facilitatepurification. For example, one construct can include a polypeptideencoding a nucleic acid sequence linked to six histidine residuesfollowed by a thioredoxin, an enterokinase cleavage site (see, e.g.,Williams, Biochemistry, 34:1787-97 (1995)), and an C-terminaltranslocation domain. The histidine residues facilitate detection andpurification while the enterokinase cleavage site provides a means forpurifying the desired protein(s) from the remainder of the fusionprotein. Technology pertaining to vectors encoding fusion proteins andapplication of fusion proteins are well described in the scientific andpatent literature (see, e.g., Kroll, DNA Cell. Biol., 12:441-53 (1993)).

Expression vectors, either as individual expression vectors or aslibraries of expression vectors, comprising the ligand-binding regionencoding sequences may be introduced into a genome or into the cytoplasmor a nucleus of a cell and expressed by a variety of conventionaltechniques, well described in the scientific and patent literature. See,e.g., Roberts, Nature, 328:731 (1987); Berger supra; Schneider, ProteinExpr. Purf., 6435:10 (1995); Sambrook; Tijssen; Ausubel. Productinformation from manufacturers of biological reagents and experimentalequipment also provide information regarding known biological methods.The vectors can be isolated from natural sources, obtained from suchsources as ATCC or GenBank libraries, or prepared by synthetic orrecombinant methods.

The nucleic acids can be expressed in expression cassettes, vectors orviruses which are stably or transiently expressed in cells (e.g.,episomal expression systems). Selection markers can be incorporated intoexpression cassettes and vectors to confer a selectable phenotype ontransformed cells and sequences. For example, selection markers can codefor episomal maintenance and replication such that integration into thehost genome is not required. For example, the marker may encodeantibiotic resistance (e.g., chloramphenicol, kanamycin, G418,bleomycin, hygromycin) or herbicide resistance (e.g., chlorosulfuron orBasta) to permit selection of those cells transformed with the desiredDNA sequences (see, e.g., Blondelet-Rouault, Gene, 190:315-17 (1997);Aubrecht, J. Pharmacol. Exp. Ther., 281:992-97 (1997)). Becauseselectable marker genes conferring resistance to substrates likeneomycin or hygromycin can only be utilized in tissue culture,chemoresistance genes are also used as selectable markers in vitro andin vivo.

A chimeric nucleic acid sequence may encode a T2R ligand-binding regionwithin any 7-transmembrane polypeptide. Because 7-transmembrane receptorpolypeptides have similar primary sequences and secondary and tertiarystructures, structural domains (e.g., extracellular domain, TM domains,cytoplasmic domain, etc.) can be readily identified by sequenceanalysis. For example, homology modeling, Fourier analysis and helicalperiodicity detection can identify and characterize the seven domainswith a 7-transmembrane receptor sequence. Fast Fourier Transform (FFT)algorithms can be used to assess the dominant periods that characterizeprofiles of the hydrophobicity and variability of analyzed sequences.Periodicity detection enhancement and alpha helical periodicity indexcan be done as by, e.g., Donnelly, Protein Sci., 2:55-70 (1993). Otheralignment and modeling algorithms are well known in the art (see, e.g.,Peitsch, Receptors Channels, 4:161-64 (1996); Kyte & Doolittle, J. Md.Biol., 157:105-32 (1982); Cronet, Protein Eng., 6:59-64 (1993);http://bioinfo.weizmann.ac.il/).

The present invention also includes not only the nucleic acid moleculesand polypeptides having the specified nucleic and amino acid sequences,but also fragments thereof, particularly fragments of e.g., 40, 60, 80,100, 150, 200, or 250 nucleotides, or more, as well as polypeptidefragments of, e.g., 10, 20, 30, 50, 70, 100, or 150 amino acids, ormore. Optionally, the nucleic acid fragments can encode an antigenicpolypeptide that is capable of binding to an antibody raised against aT2R family member. Further, a protein fragment of the invention canoptionally be an antigenic fragment that is capable of binding to anantibody raised against a T2R family member.

Also contemplated are chimeric proteins, comprising at least 10, 20, 30,50, 70, 100, or 150 amino acids, or more, of one of at least one of theT2R polypeptides described herein, coupled to additional amino acidsrepresenting all or part of another GPCR, preferably a member of the 7transmembrane superfamily. These chimeras can be made from the instantreceptors and another GPCR, or they can be made by combining two or moreof the present receptors. In one embodiment, one portion of the chimeracorresponds to, or is derived from the transmembrane domain of a T2Rpolypeptide of the invention. In another embodiment, one portion of thechimera corresponds to, or is derived from the one or more of thetransmembrane regions of a T2R polypeptide described herein, and theremaining portion or portions can come from another GPCR. Chimericreceptors are well known in the art, and the techniques for creatingthem and the selection and boundaries of domains or fragments of GProtein-Coupled Receptors for incorporation therein are also well known.Thus, this knowledge of those skilled in the art can readily be used tocreate such chimeric receptors. The use of such chimeric receptors canprovide, for example, a taste selectivity characteristic of one of thereceptors specifically disclosed herein, coupled with the signaltransduction characteristics of another receptor, such as a well knownreceptor used in prior art assay systems.

For example, a region such as a ligand-binding region, an extracellulardomain, a transmembrane domain, a transmembrane domain, a cytoplasmicdomain, an N-terminal domain, a C-terminal domain, or any combinationthereof, can be covalently linked to a heterologous protein. Forinstance, a T2R transmembrane region can be linked to a heterologousGPCR transmembrane domain, or a heterologous GPCR extracellular domaincan be linked to a T2R transmembrane region. Other heterologous proteinsof choice can include, e.g., green fluorescent protein, β-gal,glutamtate receptor, and the rhodopsin N-terminus.

Also within the scope of the invention are host cells for expressing theT2Rs, fragments, or variants of the invention. To obtain high levels ofexpression of a cloned gene or nucleic acid, such as cDNAs encoding theT2Rs, fragments, or variants of the invention, one of skill typicallysubclones the nucleic acid sequence of interest into an expressionvector that contains a strong promoter to direct transcription, atranscription/translation terminator, and if for a nucleic acid encodinga protein, a ribosome binding site for translational initiation.Suitable bacterial promoters are well known in the art and described,e.g., in Sambrook et al. However, bacterial or eukaryotic expressionsystems can be used.

Any of the well-known procedures for introducing foreign nucleotidesequences into host cells may be used. These include the use of calciumphosphate transfection, polybrene, protoplast fusion, electroporation,liposomes, microinjection, plasma vectors, viral vectors and any of theother well known methods for introducing cloned genomic DNA, cDNA,synthetic DNA or other foreign genetic material into a host cell (see,e.g., Sambrook et al.) It is only necessary that the particular genetic,engineering procedure used be capable of successfully introducing atleast one nucleic acid molecule into the host cell capable of expressingthe T2R, fragment, or variant of interest.

After the expression vector is introduced into the cells, thetransfected cells are cultured under conditions favoring expression ofthe receptor, fragment, or variant of interest, which is then recoveredfrom the culture using standard techniques. Examples of such techniquesare well known in the art. See, e.g., WO 00/06593, which is incorporatedby reference in a manner consistent with this disclosure.

D. Immunological Detection of T2Rs

In addition to the detection of T2R genes and gene expression usingnucleic acid hybridization technology, one can also use immunoassays todetect T2Rs, e.g., to identify taste receptor cells, and variants of T2Rfamily members. Immunoassays can be used to qualitatively orquantitatively analyze the T2Rs. A general overview of the applicabletechnology can be found in Harlow & Lane, Antibodies: A LaboratoryManual (1988).

1. Antibodies to T2R Family Members

Methods of producing polyclonal and monoclonal antibodies that reactspecifically with a T2R family member are known to those of skill in theart (see, e.g., Coligan, Current Protocols in Immunology (1991); Harlow& Lane, supra; Goding, Monoclonal Antibodies: Principles and Practice(2d ed. 1986); and Kohler & Milstein, Nature, 256:495-97 (1975)). Suchtechniques include antibody preparation by selection of antibodies fromlibraries of recombinant antibodies in phage or similar vectors, as wellas preparation of polyclonal and monoclonal antibodies by immunizingrabbits or mice (see, e.g., Huse et al., Science, 246:1275-81 (1989);Ward et al., Nature, 341:544-46 (1989)).

A number of T2R-comprising immunogens may be used to produce antibodiesspecifically reactive with a T2R family member. For example, arecombinant T2R protein, or an antigenic fragment thereof, can beisolated as described herein. Suitable antigenic regions include, e.g.,the consensus sequences disclosed above that can be used to identifymembers of the T2R family. Recombinant proteins can be expressed ineukaryotic or prokaryotic cells as described above, and purified asgenerally known in the art. Recombinant protein is a preferred immunogenfor the production of monoclonal or polyclonal antibodies.Alternatively, a synthetic peptide derived from the sequences disclosedherein and conjugated to a carrier protein can be used an immunogen.Naturally occurring protein may also be used either in pure or impureform. The product may then be injected into an animal capable ofproducing antibodies. Either monoclonal or polyclonal antibodies may begenerated, for subsequent use in immunoassays to measure the protein.

More specifically, methods of production of polyclonal antibodies areknown to those of skill in the art. For example, an inbred strain ofmice (e.g., BALB/C mice) or rabbits may be immunized with a T2Rpolypeptide using a standard adjuvant, such as Freund's adjuvant, and astandard immunization protocol. The animal's immune response to theimmunogen preparation may then be monitored by taking test bleeds anddetermining the titer of reactivity to the T2R. When appropriately hightiters of antibody to the immunogen are obtained, blood may be collectedfrom the animal and antisera may be prepared. Further fractionation ofthe antisera to enrich for antibodies reactive to the T2R polypeptidecan be done if desired (see Harlow & Lane, supra).

Monoclonal antibodies may be obtained by various techniques familiar tothose skilled in the art. Briefly, spleen cells from an animal immunizedwith a desired antigen may be immortalized, commonly by fusion with amyeloma cell (see Kohler & Milstein, Eur. J. Immunol., 6:511-19 (1976)).Alternative methods of immortalization include transformation withEpstein Barr Virus, oncogenes, retroviruses, or other methods well knownin the art. Colonies arising from single immortalized cells may then bescreened for production of antibodies of the desired specificity andaffinity for the antigen. Yield of the monoclonal antibodies produced bysuch cells may be enhanced by various techniques, including injectioninto the peritoneal cavity of a vertebrate host. Alternatively, one mayisolate nucleic acid sequences that encode a monoclonal antibody, or abinding fragment thereof, by screening a nucleic acid library from humanB cells according to the general protocol outlined by Huse et al.,Science, 246:1275-81 (1989).

Monoclonal antibodies and polyclonal sera are generally collected andtitered against the immunogen protein in an immunoassay, e.g., a solidphase immunoassay with the immunogen immobilized on a solid support.Typically, polyclonal antisera with a titer of 104 or greater may beselected and tested for their cross reactivity against non-T2R proteins,or even other T2R family members or other related proteins from otherorganisms, using a competitive binding immunoassay. Specific polyclonalantisera and monoclonal antibodies will usually bind with a Kd of atleast about 0.1 mM, more usually at least about 1 pM, optionally atleast about 0.1 pM or better, and optionally 0.01 pM or better.

Once T2R family member specific antibodies are available, individual T2Rproteins can be detected by a variety of immunoassay methods. For areview of immunological and immunoassay procedures, see Stites & Terreds., Basic and Clinical Immunology (7th ed. 1991). Moreover, theimmunoassays of the present invention can be performed in any of severalconfigurations, which are reviewed extensively in Maggio, ed., EnzymeImmunoassay (1980); and Harlow & Lane, supra.

2. Immunological Binding Assays

T2R proteins can be detected and/or quantified using any of a number ofwell recognized immunological binding assays (see, e.g., U.S. Pat. Nos.4,366,241; 4,376,110; 4,517,288; and 4,837,168). For a review of thegeneral immunoassays, see Asai, ed., Methods in Cell Biology: Antibodiesin Cell Biology, volume 37 (1993); Stites & Terr, eds., Basic andClinical Immunology (7th ed. 1991). Immunological binding assays (orimmunoassays) typically use an antibody that specifically binds to aprotein or antigen of choice (in this case a T2R family member or anantigenic subsequence thereof). The antibody (e.g., anti-T2R) may beproduced by any of a number of means well known to those of skill in theart, as described above.

Immunoassays also often use a labeling agent to specifically bind to,and label the complex formed by the antibody and antigen. The labelingagent may itself be one of the moieties comprising the antibody/antigencomplex. Thus, the labeling agent may be a labeled T2R polypeptide or alabeled anti-T2R antibody. Alternatively, the labeling agent may be athird moiety, e.g., a secondary antibody, that specifically binds to theantibody/T2R complex (a secondary antibody is typically specific toantibodies of the species from which the first antibody is derived).Other proteins capable of specifically binding immunoglobulin constantregions, such as protein A or protein G may also be used as the labelagent. These proteins exhibit a strong non-immunogenic reactivity withimmunoglobulin constant regions from a variety of species (see, e.g.,Kronval et al., J. Immunol., 111:1401-06 (1973); Akerstrom et al., J.Immunol., 135:2589-642 (1985)). The labeling agent can be modified witha detectable moiety, such as biotin, to which another molecule canspecifically bind, such as streptavidin. A variety of detectablemoieties are well known to those skilled in the art.

Throughout the assays, incubation and/or washing steps may be requiredafter each combination of reagents. Incubation steps can vary from about5 seconds to several hours, optionally from about 5 minutes to about 24hours. However, the incubation time will generally depend upon the assayformat, antigen, volume of solution, concentrations, and the like.Usually, the assays will be carried out at ambient temperature, althoughthey can be conducted over a range of temperatures, e.g., from about 10°C. to about 40° C.

a. Non-Competitive Assay Formats

Immunoassays for detecting a T2R protein in a sample may be eithercompetitive or noncompetitive. Noncompetitive immunoassays are assays inwhich the amount of antigen is directly measured. In one preferred“sandwich” assay, for example, the anti-T2R antibodies can be bounddirectly to a solid substrate on which they are immobilized. Theseimmobilized antibodies may then capture any T2R protein present in thetest sample. The T2R protein is thus immobilized, and is then bound by alabeling agent, such as a second T2R antibody bearing a label.Alternatively, the second antibody may lack a label, but it may, inturn, be bound by a labeled third antibody specific to antibodies of thespecies from which the second antibody is derived. The second or thirdantibody is typically modified with a detectable moiety, such as biotin,to which another molecule specifically binds, e.g., streptavidin, toprovide a detectable moiety.

b. Competitive Assay Formats

In competitive assays, the amount of T2R protein present in the sampleis measured indirectly by measuring the amount of a known, added(exogenous) T2R protein displaced (competed away) from an anti-T2Rantibody by the unknown T2R protein present in a sample. In onecompetitive assay, a known amount of T2R protein is added to a sample,and the sample is then contacted with an antibody that specificallybinds to the T2R. The amount of exogenous T2R protein bound to theantibody is inversely proportional to the concentration of T2R proteinpresent in the sample. In a particularly preferred embodiment, theantibody is immobilized on a solid substrate. The amount of T2R proteinbound to the antibody may be determined either by measuring the amountof T2R protein present in a T2R/antibody complex, or alternatively bymeasuring the amount of remaining uncomplexed protein. The amount of T2Rprotein may be detected by providing a labeled T2R molecule.

A hapten inhibition assay is another preferred competitive assay. Inthis assay the known T2R protein is immobilized on a solid substrate. Aknown amount of anti-T2R antibody is added to the sample, and the sampleis then contacted with the immobilized T2R. The amount of anti-T2Rantibody bound to the known immobilized T2R protein is inverselyproportional to the amount of T2R protein present in the sample. Again,the amount of immobilized antibody may be detected by detecting eitherthe immobilized fraction of antibody or the fraction of the antibodythat remains in solution. Detection may be direct where the antibody islabeled, or indirect by the subsequent addition of a labeled moiety thatspecifically binds to the antibody as described above.

c. Cross-Reactivity Determinations

Immunoassays in the competitive binding format can also be used forcross-reactivity determinations. For example, a protein at leastpartially encoded by the nucleic acid sequences disclosed herein can beimmobilized to a solid support. Proteins (e.g., T2R polypeptides andhomologs thereof) may be added to the assay and thereby compete forbinding of the antisera to the immobilized antigen. The ability of theadded proteins to compete for binding of the antisera to the immobilizedprotein is compared to the ability of the T2R polypeptide encoded by thenucleic acid sequences disclosed herein to compete with itself. Thepercent cross-reactivity for the above proteins is calculated, usingstandard calculations. Those antisera with less than 10%cross-reactivity with each of the added proteins listed above areselected and pooled. The cross-reacting antibodies are optionallyremoved from the pooled antisera by immunoabsorption with the addedconsidered proteins, e.g., distantly related homologs. In addition,peptides comprising amino acid sequences representing consensussequences that may be used to identify members of the T2R family can beused in cross-reactivity determinations.

The immunoabsorbed and pooled antisera may then be used in a competitivebinding immunoassay as described above to compare a second protein,thought to be perhaps an allele or polymorphic variant of a T2R familymember, to the immunogen protein (i.e., T2R protein encoded by thenucleic acid sequences disclosed herein). In order to make thiscomparison, the two proteins are each assayed at a wide range ofconcentrations and the amount of each protein required to inhibit 50% ofthe binding of the antisera to the immobilized protein is determined. Ifthe amount of the second protein required to inhibit 50% of binding isless than 10 times the amount of the protein encoded by nucleic acidsequences disclosed herein required to inhibit 50% of binding, then thesecond protein is said to specifically bind to the polyclonal antibodiesgenerated to a T2R immunogen.

Antibodies raised against T2R consensus sequences can also be used toprepare antibodies that specifically bind only to GPCRs of the T2Rfamily, but not to GPCRs from other families. For example, polyclonalantibodies that specifically bind to a particular member of the T2Rfamily can be made by subtracting out cross-reactive antibodies usingother T2R family members. Species-specific polyclonal antibodies can bemade in a similar way. For example, antibodies specific to human T2R1can be made by, subtracting out antibodies that are cross-reactive withorthologous sequences, e.g., rat T2R1 or mouse T2R1.

d. Other Assay Formats

Western blot (immunoblot) analysis may be used to detect and quantifythe presence of T2R protein in a sample. The technique generallycomprises separating sample proteins by gel electrophoresis on the basisof molecular weight, transferring the separated proteins to a suitablesolid support, (e.g., a nitrocellulose filter, a nylon filter, orderivatized nylon filter), and incubating the sample with antibodiesthat specifically bind the T2R protein. The anti-T2R polypeptideantibodies then specifically bind to the T2R polypeptide on the solidsupport. These antibodies may be directly labeled, or alternatively maybe subsequently detected using labeled antibodies (e.g., labeled sheepanti-mouse antibodies) that specifically bind to the anti-T2Rantibodies.

Other, assay formats include liposome immunoassays (LIA), which useliposomes designed to bind specific molecules (e.g., antibodies) andrelease encapsulated reagents or markers. The released chemicals arethen detected according to standard techniques (see Monroe et al., Amer.Clin. Prod. Rev., 5:34-41 (1986)).

e. Reduction of Non-Specific Binding

One of skill in the art will appreciate that it is often desirable tominimize non-specific binding in immunoassays. Particularly, where theassay involves an antigen or antibody immobilized on a solid substrateit is desirable to minimize the amount of non-specific binding to thesubstrate. Means of reducing such non-specific binding are well known tothose of skill in the art. Typically, these techniques involve coatingthe substrate with a proteinaceous composition. In particular, proteincompositions such as bovine serum albumin (BSA), nonfat powdered milk,and gelatin are widely used, with powdered milk being most preferred.

f. Labels

The particular label or detectable group used in the assay is not acritical aspect of the invention, as long as it does not significantlyinterfere with the specific binding of the antibody used in the assay.The detectable group can be any material having a detectable physical orchemical property. Such detectable labels have been well developed inthe field of immunoassays and, in general, most any label useful in suchmethods can be applied to the present invention. Thus, a label is anycomposition detectable by spectroscopic, photochemical, biochemical,immunochemical, electrical, optical, or chemical means. Useful labels inthe present invention include magnetic beads (e.g., DYNABEADS™),fluorescent dyes (e.g., fluorescein isothiocyanate, Texas red,rhodamine, and the like), radiolabels (e.g., ³H, ¹²⁵I, ³⁵S, ¹⁴C, or³²P), enzymes (e.g., horseradish peroxidase, alkaline phosphatase andothers commonly used in an ELISA), and colorimetric labels such ascolloidal gold or colored glass or plastic beads (e.g., polystyrene,polypropylene, latex, etc.).

The label may be coupled directly or indirectly to the desired componentof the assay according to methods well known in the art. As indicatedabove, a wide variety of labels may be used, with the choice of labeldepending on sensitivity required, ease of conjugation with thecompound, stability requirements, available instrumentation, anddisposal provisions.

Non-radioactive labels are often attached by indirect means. Generally,a ligand molecule (e.g., biotin) is covalently bound to the molecule.The ligand then binds to another molecules (e.g., streptavidin)molecule, which is either inherently detectable or covalently bound to asignal system, such as a detectable enzyme, a fluorescent compound, or achemiluminescent compound. The ligands and their targets can be used inany suitable combination with antibodies that recognize a T2R protein,or secondary antibodies that recognize anti-T2R.

The molecules can also be conjugated directly to signal generatingcompounds, e.g., by conjugation with an enzyme or fluorophore. Enzymesof interest as labels will primarily be hydrolases, particularlyphosphatases, esterases and glycosidases, or oxidotases, particularlyperoxidases. Fluorescent compounds include fluorescein and itsderivatives, rhodamine and its derivatives, dansyl, umbelliferone, etc.Chemiluminescent compounds include luciferin, and2,3-dihydrophthalazinediones, e.g., luminol. For a review of variouslabeling or signal producing systems that may be used, see U.S. Pat. No.4,391,904.

Means of detecting labels are well known to those of skill in the art.Thus, e.g., where the label is a radioactive label, means for detectioninclude a scintillation counter or photographic film as inautoradiography. Where the label is a fluorescent label, it may bedetected by exciting the fluorochrome with the appropriate wavelength oflight and detecting the resulting fluorescence. The fluorescence may bedetected visually, by means of photographic film, by the use ofelectronic detectors such as charge-coupled devices (CCDs) orphotomultipliers and the like. Similarly, enzymatic labels may bedetected by providing the appropriate substrates for the enzyme anddetecting the resulting reaction product. Finally simple colorimetriclabels may be detected simply by observing the color associated with thelabel. Thus, in various dipstick assays, conjugated gold often appearspink, while various conjugated beads appear the color of the bead.

Some assay formats do not require the use of labeled components. Forinstance, agglutination assays can be used to detect the presence of thetarget antibodies. In this case, antigen coated particles areagglutinated by samples comprising the target antibodies. In thisformat, none of the components need be labeled and the presence of thetarget antibody is detected by simple visual inspection.

E. Detection of Taste Modulators

Methods and compositions for determining whether a test compoundspecifically binds to a T2R polypeptide of the invention, both in vitroand in vivo are described below. Many aspects of cell physiology can bemonitored to assess the effect of ligand-binding to a naturallyoccurring or chimeric T2Rs. These assays may be performed on intactcells expressing a T2R polypeptide, on permeabilized cells, or onmembrane fractions produced by standard methods.

Taste receptors bind tastants and initiate the transduction of chemicalstimuli into electrical signals. An activated or inhibited G Proteinwill in turn alter the properties of target enzymes, channels, and othereffector proteins. Some examples are the activation of cGMPphosphodiesterase by transducing in the visual system, adenylate cyclaseby the stimulatory G Protein, phospholipase C by Gq and other cognate GProteins, and modulation of diverse channels by Gi and other G Proteins.Downstream consequences can also be examined such as generation ofdiacyl glycerol and IP3 by phospholipase C, and in turn, for calciummobilization by IP3.

The T2R proteins or polypeptides of the assay will typically be selectedfrom a polypeptide having a sequence of SEQ ID NOS: 2, 4, 6, 8, 10, 12,14, 16, 18, 20, and 24, or fragments or conservatively modified variantsthereof.

Alternatively, the T2R proteins of polypeptides of the assay can bederived from a eukaryote host cell, and can include an amino acidsubsequence having amino acid sequence identity to SEQ ID NOS: 2, 4, 6,8, 10, 12, 14, 16, 18, 20, and 24, or conservatively modified variantsthereof. Generally, the amino acid sequence identity will be at least30% preferably 30-40%, more specifically 50-60, 70%, 75%, 80%, 85%, 90%,95%, 96%, 97%, 98%, or 99%. Optionally, the T2R proteins or polypeptidesof the assays can comprise a region of a T2R polypeptide, such as anextracellular domain, transmembrane region, cytoplasmic domain,ligand-binding domain, and the like. Optionally, the T2R polypeptide, ora portion thereof, can be covalently linked to a heterologous protein tocreate a chimeric protein used in the assays described herein.

Modulators of T2R activity may be tested using T2R proteins orpolypeptides as described above, either recombinant or naturallyoccurring. The T2R proteins or polypeptides can be isolated, expressedin a cell, expressed in a membrane derived from a cell, expressed intissue or in an animal, either recombinant or naturally occurring. Forexample, tongue slices, dissociated cells from a tongue, transformedcells, or membranes can be used. Modulation can be tested using one ofthe in vitro or in vivo assays described herein.

1. In Vitro Binding Assays

Taste transduction can also be examined in vitro with soluble or solidstate reactions, using a T2R polypeptide or a chimeric molecule, such asan extracellular domain, transmembrane region, or combination thereof,of a T2R covalently linked to a heterologous signal transduction domain;or a heterologous extracellular domain and/or transmembrane regioncovalently linked to the transmembrane and/or cytoplasmic domain of aT2R protein or polypeptide. Furthermore, ligand-binding regions of a T2Rpolypeptide can be used in vitro in soluble or solid state reactions toassay for ligand binding. In numerous embodiments, a chimeric receptorcan be made that comprises all or part of a T2R polypeptide, as well anadditional sequence that facilitates the localization of the T2R to themembrane, such as a rhodopsin, e.g., an N-terminal fragment of arhodopsin protein.

Ligand binding to a T2R protein, a ligand-binding region, or chimericprotein can be tested in solution, in a bilayer membrane, attached to asolid phase, in a lipid monolayer, or in vesicles. Binding of amodulator can be tested using, e.g., changes in spectroscopiccharacteristics (e.g., fluorescence, absorbance, refractive index)hydrodynamic (e.g., shape), chromatographic, or solubility properties.

T2R-G Protein interactions can also be examined. For example, binding ofthe G Protein to the T2R polypeptide or its release from the polypeptidecan be examined. In the absence of GTP, an activator will lead to theformation of a tight complex of a G protein (all three subunits) withthe T2R. This complex can be detected in a variety of ways, as notedabove. Such an assay can be modified to search for inhibitors, e.g., byadding an activator to the T2R and G protein in the absence of GTP,which form a tight complex, and then screen for inhibitors by looking atdissociation of the T2R-G protein complex. In the presence of GTP,release of the alpha subunit of the G protein from the other two Gprotein subunits serves as a criterion of activation.

In another embodiment of the invention, a GTPγS assay may be used. Asdescribed above, upon activation of a GPCR, the Gα subunit of the Gprotein complex is stimulated to exchange bound GDP for GTP.Ligand-mediated stimulation of G protein exchange activity can bemeasured in a biochemical assay measuring the binding of addedradioactively-labeled GTPγ³⁵S to the G protein in the presence of aputative ligand. Typically, membranes containing the chemosensoryreceptor of interest are mixed with a complex of G proteins. Potentialinhibitors and/or activators and GTPγS are added to the assay, andbinding of GTPγS to the G protein is measured. Binding can be measuredby liquid scintillation counting or by any other means known in the art,including scintillation proximity assays (SPA). In other assays formats,fluorescently-labeled GTPγS can be utilized.

In particularly preferred embodiments, T2R-gustducin interactions may bemonitored as a function of T2R receptor activation. For instance, mouseT2R5 shows strong cycloheximide dependent coupling with gustducin. Suchligand dependent coupling of T2R receptors with gustducin can be used asa marker to identify modifiers of any member of the T2R family.

2. Fluorescence Polarization Assays

In another embodiment, Fluorescence Polarization (“FP”) based assays maybe used to detect and monitor ligand binding. Fluorescence polarizationis a versatile laboratory technique for measuring equilibrium binding,nucleic acid hybridization, and enzymatic activity. Fluorescencepolarization assays are homogeneous in that they do not require aseparation step such as centrifugation, filtration, chromatography,precipitation, or electrophoresis. These assays are done in real time,directly in solution and do not require an immobilized phase.Polarization values can be measured repeatedly and after the addition ofreagents since measuring the polarization is rapid and does not destroythe sample. Generally, this technique can be used to measurepolarization values of fluorophores from low picomolar to micromolarlevels. This section describes how fluorescence polarization can be usedin a simple and quantitative way to measure the binding of ligands tothe T2R polypeptides of the invention.

When a fluorescently labeled molecule is excited with plane polarizedlight, it emits light that has a degree of polarization that isinversely proportional to its molecular rotation. Large fluorescentlylabeled molecules remain relatively stationary during the excited state(4 nanoseconds in the case of fluorescein) and the polarization of thelight remains relatively constant between excitation and emission. Smallfluorescently labeled molecules rotate rapidly during the excited stateand the polarization changes significantly between excitation andemission. Therefore, small molecules have low polarization values andlarge molecules have high polarization values. For example, asingle-stranded fluorescein-labeled oligonucleotide has a relatively lowpolarization value but when it is hybridized to a complementary strand,it has a higher polarization value. When using FP to detect and monitortastant-binding which may activate or inhibit the chemosensory receptorsof the invention, fluorescence-labeled tastants or auto-fluorescenttastants may be used.

Fluorescence polarization (P) is defined as:

$P = \frac{{Int}_{U} - {Int}_{\bot}}{{Int}_{U} - {Int}_{\bot}}$

Where Π is the intensity of the emission light parallel to theexcitation light plane and Int ⊥ is the intensity of the emission lightperpendicular to the excitation light plane. P, being a ratio of lightintensities, is a dimensionless number. For example, the Beacon andBeacon 2000™ System may be used in connection with these assays. Suchsystems typically express polarization in millipolarization units (1Polarization Unit=1000 mP Units).

The relationship between molecular rotation and size is described by thePerrin equation. Summarily, the Perrin equation states that polarizationis directly proportional to the rotational relaxation time, the timethat it takes a molecule to rotate through an angle of approximately68.5° Rotational relaxation time is related to viscosity (η), absolutetemperature (T), molecular volume (V), and the gas constant (R) by thefollowing equation:

${RotationalRelaxationTime} = \frac{3\eta\; V}{RT}$

The rotational relaxation time is small (≈1 nanosecond) for smallmolecules (e.g. fluorescein) and large (≈100 nanoseconds) for largemolecules (e.g. immunoglobulins). If viscosity and temperature are heldconstant, rotational relaxation time, and therefore polarization, isdirectly related to the molecular volume.

Changes in molecular volume may be due to interactions with othermolecules, dissociation, polymerization, degradation, hybridization, orconformational changes of the fluorescently labeled molecule. Forexample, fluorescence polarization has been used to measure enzymaticcleavage of large fluorescein labeled polymers by proteases, DNases, andRNases. It also has been used to measure equilibrium binding forprotein/protein interactions, antibody/antigen binding, and protein/DNAbinding.

3. Solid State and Soluble High Throughput Assays

In yet another embodiment, the invention provides soluble assays using aT2R polypeptide; or a cell or tissue expressing a T2R polypeptide. Inanother embodiment, the invention provides solid phase based in vitroassays in a high throughput format, where the T2R polypeptide, or cellor tissue expressing the T2R polypeptide is attached to a solid phasesubstrate.

In the high throughput assays of the invention, it is possible to screenup to several thousand different modulators or ligands in a single day.In particular, each well of a microtiter plate can be used to run aseparate assay against a selected potential modulator, or, ifconcentration or incubation time effects are to be observed, every 5-10wells can test a single modulator. Thus, a single standard microtiterplate can assay about 100 (e.g., 96) modulators. If 1536 well plates areused, then a single plate can easily assay from about 1000 to about 1500different compounds. It is also possible to assay multiple compounds ineach plate well. Further, it is possible to assay several differentplates per day allowing for assay screens of about 6,000-20,000compounds per day. More recently, microfluidic approaches to reagentmanipulation have been developed.

The molecule of interest can be bound to the solid state component,directly or indirectly, via covalent or non-covalent linkage, e.g., viaa tag. The tag can be any of a variety of components. In general, amolecule which binds the tag (a tag binder) is fixed to a solid support,and the tagged molecule of interest (e.g., the taste transductionmolecule of interest) is attached to the solid support by interaction ofthe tag and the tag binder.

A number of tags and tag binders can be used, based upon known molecularinteractions well described in the literature. For example, where a taghas a natural binder, for example, biotin, protein A, or protein G, itcan be used in conjunction with appropriate tag binders (avidin,streptavidin, neutravidin, the Fc region of an immunoglobulin, etc.).Antibodies to molecules with natural binders such as biotin are alsowidely available and appropriate tag binders (see, SIGMA Immunochemicals1998 catalogue, SIGMA, St. Louis Mo.).

Similarly, any haptenic or antigenic compound can be used in combinationwith an appropriate antibody to form a tag/tag binder pair. Thousands ofspecific antibodies are commercially available and many additionalantibodies are described in the literature. For example, in one commonconfiguration, the tag is a first antibody and the tag binder is asecond antibody which recognizes the first antibody. In addition toantibody-antigen interactions, receptor-ligand interactions are alsoappropriate as tag and tag-binder pairs. For example, agonists andantagonists of cell membrane receptors (e.g., cell receptor-ligandinteractions such as transferrin, c-kit, viral receptor ligands,cytokine receptors, chemokine receptors, interleukin receptors,immunoglobulin receptors and antibodies, the cadherein family, theintegrin family, the selectin family, and the like; see, e.g., Pigott &Power, The Adhesion Molecule Facts Book I (1993)). Similarly, toxins andvenoms, viral epitopes, hormones (e.g., opiates, steroids, etc.),intracellular receptors (e.g., which mediate the effects of varioussmall ligands, including steroids, thyroid hormone, retinoids andvitamin D; peptides), drugs, lectins, sugars, nucleic acids (both linearand cyclic polymer configurations), oligosaccharides, proteins,phospholipids and antibodies can all interact with various cellreceptors.

Synthetic polymers, e.g., polyurethanes, polyesters, polycarbonates,polyureas, polyamides, polyethyleneimines, polyarylene sulfides,polysiloxanes, polyimides, and polyacetates, can also form anappropriate tag or tag binder. Many other tag/tag binder pairs are alsouseful in assay systems described herein, as would be apparent to one ofskill upon review of this disclosure.

Common linkers such as peptides, polyethers, and the like can also serveas tags, and include polypeptide sequences, such as poly gly sequencesof between about 5 and 200 amino acids. Such flexible linkers are knownto persons of skill in the art. For example, poly(ethelyne glycol)linkers are available from Shearwater Polymers, Inc. Huntsville, Ala.These linkers optionally have amide linkages, sulfhydryl linkages, orheterofunctional linkages.

Tag binders may be fixed to solid substrates using any of a variety ofmethods currently available. Solid substrates are commonly derivatizedor functionalized by exposing all or a portion of the substrate to achemical reagent which fixes a chemical group to the surface that isreactive with a portion of the tag binder. For example, groups that aresuitable for attachment to a longer chain portion include amines,hydroxyl, thiol, and carboxyl groups. Aminoalkylsilanes andhydroxyalkylsilanes can be used to functionalize a variety of surfaces,such as glass surfaces. The construction of such solid phase biopolymerarrays is well described in the literature. See, e.g., Merrifield, J.Am. Chem. Soc., 85:2149-54 (1963) (describing solid phase synthesis of,e.g., peptides); Leysen et al., J. Immun. Meth., 102:259-74 (1987)(describing synthesis of solid phase components on pins); Frank &Doring, Tetrahedron, 44:60316040 (1988) (describing synthesis of variouspeptide sequences on cellulose disks); Fodor et al., Science, 251:767-77(1991); Sheldon et al., Clinical Chemistry, 39(4):718-19 (1993); andKozal et al., Nature Medicine, 2(7):753759 (1996) (all describing arraysof biopolymers fixed to solid substrates). Non-chemical approaches forfixing tag binders to substrates include other common methods, such asheat, cross-linking by UV radiation, and the like.

4. Computer-Based Assays

Yet another assay for compounds that modulate T2R polypeptide activityinvolves computer assisted compound design, in which a computer systemis used to generate a three-dimensional structure of an T2R polypeptidebased on the structural information encoded by its amino acid sequence.The input amino acid sequence interacts directly and actively with apreestablished algorithm in a computer program to yield secondary,tertiary, and quaternary structural models of the protein. The models ofthe protein structure are then examined to identify regions of thestructure that have the ability to bind, e.g., ligands. These regionsare then used to identify ligands that bind to the protein.

The three-dimensional structural model of the protein is generated byentering protein amino acid sequences of at least 10 amino acid residuesor corresponding nucleic acid sequences encoding a T2R polypeptide intothe computer system. The nucleotide sequence encoding the T2Rpolypeptide, or the amino acid sequence thereof, can be any sequencedisclosed herein, and conservatively modified versions thereof.

The amino acid sequence represents the primary sequence or subsequenceof the protein, which encodes the structural information of the protein.At least 10 residues of the amino acid sequence (or a nucleotidesequence encoding 10 amino acids) are entered into the computer systemfrom computer keyboards, computer readable substrates that include, butare not limited to, electronic storage media (e.g., magnetic diskettes,tapes, cartridges, and chips), optical media (e.g., CD ROM), informationdistributed by internet sites, and by RAM. The three-dimensionalstructural model of the protein is then generated by the interaction ofthe amino acid sequence and the computer system, using software known tothose of skill in the art.

The amino acid sequence represents a primary structure that encodes theinformation necessary to form the secondary, tertiary and quaternarystructure of the protein of interest. The software looks at certainparameters encoded by the primary sequence to generate the structuralmodel. These parameters are referred to as “energy terms,” and primarilyinclude electrostatic potentials, hydrophobic potentials, solventaccessible surfaces, and hydrogen bonding. Secondary energy termsinclude van der Waals potentials. Biological molecules form thestructures that minimize the energy terms in a cumulative fashion. Thecomputer program is therefore using these terms encoded by the primarystructure or amino acid sequence to create the secondary structuralmodel.

The tertiary structure of the protein encoded by the secondary structureis then formed on the basis of the energy terms of the secondarystructure. The user at this point can enter additional variables such aswhether the protein is membrane bound or soluble, its location in thebody, and its cellular location, e.g., cytoplasmic, surface, or nuclear.These variables along with the energy terms of the secondary structureare used to form the model of the tertiary structure. In modeling thetertiary structure, the computer program matches hydrophobic faces ofsecondary structure with like, and hydrophilic faces of secondarystructure with like.

Once the structure has been generated, potential ligand-binding regionsare identified by the computer system. Three-dimensional structures forpotential ligands are generated by entering amino acid or nucleotidesequences or chemical formulas of compounds, as described above. Thethree-dimensional structure of the potential ligand is then compared tothat of the T2R polypeptide to identify ligands that bind to theprotein. Binding affinity between the protein and ligands is determinedusing energy terms to determine which ligands have an enhancedprobability of binding to the protein.

Computer systems are also used to screen for mutations, polymorphicvariants, alleles, and interspecies homologs of T2R genes. Suchmutations can be associated with disease states or genetic traits. Asdescribed above, GeneChip™ and related technology can also be used toscreen for mutations, polymorphic variants, alleles, and interspecieshomologs. Once the variants are identified, diagnostic assays can beused to identify patients having such mutated genes. Identification ofthe mutated T2R genes involves receiving input of a first nucleic acidor amino acid sequence of a T2R gene, or conservatively modifiedversions thereof. The sequence is entered into the computer system asdescribed above. The first nucleic acid or amino acid sequence is thencompared to a second nucleic acid or amino acid sequence that hassubstantial identity to the first sequence. The second sequence isentered into the computer system in the manner described above. Once thefirst and second sequences are compared, nucleotide or amino aciddifferences between the sequences are identified. Such sequences canrepresent allelic differences in various T2R genes, and mutationsassociated with disease states and genetic traits.

5. Cell-Based Binding Assays

In a preferred embodiment, a T2R protein or polypeptide is expressed ina eukaryotic cell as a chimeric receptor with a heterologous, chaperonesequence that facilitates its maturation and targeting through thesecretory pathway. In a preferred embodiment, the heterologous sequenceis a rhodopsin sequence, such as an N-terminal fragment of a rhodopsin.Such chimeric T2R proteins can be expressed in any eukaryotic cell, suchas HEK-293 cells. Preferably, the cells comprise a functional G Protein,e.g., Gal 5, that is capable of coupling the chimeric receptor to anintracellular signaling pathway or to a signaling protein such asphospholipase C. Activation of such chimeric receptors in such cells canbe detected using any standard method, such as by detecting changes inintracellular calcium by detecting FURA-2 dependent fluorescence in thecell.

Activated GPCR receptors become substrates for kinases thatphosphorylate the C-terminal tail of the receptor (and possibly othersites as well). Thus, activators will promote the transfer of ³²P fromgamma-labeled GTP to the receptor, which can be assayed with ascintillation counter. The phosphorylation of the C-terminal tail willpromote the binding of arrestin-like proteins, and will interfere withthe binding of G Proteins. The kinase/arrestin pathway plays a key rolein the desensitization of many GPCRs. For example, compounds thatmodulate the duration a taste receptor stays active may be useful as ameans of prolonging a desired taste or cutting off an unpleasant one.For a general review of GPCR signal transduction and methods of assayingsignal transduction, see, e.g., Methods in Enzymology, vols. 237 and 238(1994) and volume 96 (1983); Bourne et al., Nature, 10:349:117-27(1991); Bourne et al., Nature, 348:125-32 (1990); Pitcher et al, Annu.Rev. Biochem., 67:653-92 (1998).

T2R modulation may be assayed by comparing the response of a T2Rpolypeptide treated with a putative T2R modulator to the response of anuntreated control sample. Such putative T2R modulators can includetastants that either inhibit or activate T2R polypeptide activity. Inone embodiment, control samples (untreated with activators orinhibitors) are assigned a relative T2R activity value of 100.Inhibition of a T2R polypeptide is achieved when the T2R activity valuerelative to the control is about 90%, optionally 50% or 25-0%.Activation of a T2R polypeptide is achieved when the T2R activity valuerelative to the control is 110%, optionally 150%, 200-500%, or1000-2000%.

Changes in ion flux may be assessed by determining changes in ionicpolarization (i.e., electrical potential) of the cell or membraneexpressing a T2R polypeptide. One means to determine changes in cellularpolarization is by measuring changes in current (thereby measuringchanges in polarization) with voltage-clamp and patch-clamp techniques(see, e.g., the “cell-attached” mode, the “inside-out” mode, and the“whole cell” mode, e.g., Ackerman et al., New Engl. J Med., 336:1575-95(1997)). Whole cell currents are conveniently determined using knownstandards. Other known assays include: radiolabeled ion flux assays andfluorescence assays using voltage-sensitive dyes (see, e.g.,Vestergarrd-Bogind et al., J. Membrane Biol., 88:67-75 (1988); Gonzales& Tsien, Chem. Biol., 4:269-77 (1997); Daniel et al., J. Pharmacol.Meth., 25:185-93 (1991); Holevinsky et al., J. Membrane Biology,137:59-70 (1994)). Generally, the compounds to be tested are present inthe range from 1 pM to 100 mM.

The effects of test compounds upon the function of the T2R polypeptidescan be measured by examining any of the parameters described above. Anysuitable physiological change that affects GPCR activity can be used toassess the influence of a test compound on the T2R polypeptides of thisinvention. When the functional consequences are determined using intactcells or animals, one can also measure a variety of effects such astransmitter release, hormone release, transcriptional changes to bothknown and uncharacterized genetic markers (e.g., northern blots),changes in cell metabolism such as cell growth or pH changes, andchanges in intracellular second messengers such as Ca²⁺, IP3, cGMP, orcAMP.

Preferred assays for GPCRs include cells that are loaded with ion orvoltage sensitive dyes to report receptor activity. Assays fordetermining activity of such receptors can also use known agonists andantagonists for other G Protein-Coupled Receptors as negative orpositive controls to assess activity of tested compounds. In assays foridentifying modulatory compounds (e.g., agonists, antagonists), changesin the level of ions in the cytoplasm or membrane voltage may bemonitored using an ion sensitive or membrane voltage fluorescentindicator, respectively. Among the ion-sensitive indicators and voltageprobes that may be employed are those disclosed in the Molecular Probes1997 Catalog. For GPCRs, promiscuous G proteins such as Gα15 and Gα16can be used in the assay of choice (Wilkie et al, PNAS, 88:10049-53(1991)). Such promiscuous G proteins allow coupling of a wide range ofreceptors.

Receptor activation typically initiates subsequent intracellular events,e.g., increases in second messengers such as IP3, which releasesintracellular stores of calcium ions. Activation of some GPCRsstimulates the formation of inositol triphosphate (IP3) throughphospholipase C-mediated hydrolysis of phosphatidylinositol (Berridge &Irvine, Nature, 312:315-21 (1984)). IP3 in turn stimulates the releaseof intracellular calcium ion stores. Thus, a change in cytoplasmiccalcium ion levels, or a change in second messenger levels such as IP3can be used to assess GPCR function. Cells expressing such GPCRs mayexhibit increased cytoplasmic calcium levels as a result of contributionfrom both intracellular stores and via activation of ion channels, inwhich case it may be desirable although not necessary to conduct suchassays in calcium-free buffer, optionally supplemented with a chelatingagent such as EGTA, to distinguish fluorescence response resulting fromcalcium release from internal stores.

Other assays can involve determining the activity of receptors which,when activated, result in a change in the level of intracellular cyclicnucleotides, e.g., cAMP or cGMP, by activating or inhibiting enzymessuch as adenylate cyclase. There are cyclic nucleotide-gated ionchannels, e.g., rod photoreceptor cell channels and olfactory neuronchannels that are permeable to cations upon activation by binding ofcAMP or cGMP (see, e.g., Altenhofen et al., PNAS, 88:9868-72 (1991);Dhallan et al., Nature, 347:184-87 (1990)). In cases where activation ofthe receptor results in a decrease in cyclic nucleotide levels, it maybe preferable to expose the cells to agents that increase intracellularcyclic nucleotide levels, e.g., forskolin, prior to adding areceptor-activating compound to the cells in the assay. Cells for thistype of assay can be made by co-transfection of a host cell with DNAencoding a cyclic nucleotide-crated ion channel, GPCR phosphatase andDNA encoding a receptor (e.g., certain glutamate receptors, muscarinicacetylcholine receptors, dopamine receptors, serotonin receptors, andthe like), which, when activated, causes a change in cyclic nucleotidelevels in the cytoplasm.

In a preferred embodiment, T2R polypeptide activity is measured byexpressing a T2R gene in a heterologous cell with a promiscuous Gprotein that links the receptor to a phospholipase C signal transductionpathway (see Offermanns & Simon, J. Biol. Chem., 270:15175-80 (1995)).Optionally the cell line is HEK-293 (which does not naturally expressT2R genes) and the promiscuous G protein is Gα15 (Offermanns & Simon,supra). Modulation of taste transduction may be assayed by measuringchanges in intracellular Ca²⁺ levels, which change in response tomodulation of the T2R signal transduction pathway via administration ofa molecule that associates with a T2R polypeptide. Changes in Ca²⁺levels are optionally measured using fluorescent Ca²⁺ indicator dyes andfluorometric imaging.

In one embodiment, the changes in intracellular cAMP or cGMP can bemeasured using immunoassays. The method described in Offermanns & Simon,J. Bio. Chem., 270:15175-180 (1995), may be used to determine the levelof cAMP. Also, the method described in Felley-Bosco et al., Am. J. Resp.Cell and Mol. Biol., 11:159-64 (1994), may be used to determine thelevel of cGMP. Further, an assay kit for measuring cAMP and/or cGMP isdescribed in U.S. Pat. No. 4,115,538, herein incorporated by reference.

In another embodiment, phosphatidyl inositol (PI) hydrolysis can beanalyzed according to U.S. Pat. No. 5,436,128, herein incorporated byreference. Briefly, the assay involves labeling of cells with³H-myoinositol for 48 or more hrs. The labeled cells are treated with atest compound for one hour. The treated cells are lysed and extracted inchloroform-methanol-water, after which the inositol phosphates areseparated by ion exchange chromatography and quantified by scintillationcounting.

Fold stimulation is determined by calculating the ratio of cpm in thepresence of agonist, to cpm in the presence of buffer control. Likewise,fold inhibition is determined by calculating the ratio of cpm in thepresence of antagonist, to cpm in the presence of buffer control (whichmay or may not contain an agonist).

In another embodiment, transcription levels can be measured to assessthe effects of a test compound on signal transduction. A host cellcontaining a T2R polypeptide may be contacted with a test compound for asufficient time to effect any interactions, and then the level of geneexpression of a protein of interest is measured. The amount of time toeffect such interactions may be empirically determined, such as byrunning a time course and measuring the level of transcription as afunction of time. The amount of transcription may be measured by usingany method known to those of skill in the art to be suitable. Forexample, mRNA expression of the protein of interest may be detectedusing northern blots or their polypeptide products may be identifiedusing immunoassays. Alternatively, transcription based assays usingreporter gene may be used as described in U.S. Pat. No. 5,436,128,herein incorporated by reference. The reporter genes can be, e.g.,chloramphenicol acetyltransferase, luciferase, ′3-galactosidase andalkaline phosphatase. Furthermore, the protein of interest can be usedas an indirect reporter via attachment to a second reporter such asgreen fluorescent protein (see, e.g., Mistili & Spector, NatureBiotechnology, 15:961-64 (1997)).

The amount of transcription is then compared to the amount oftranscription in either the same cell in the absence of the testcompound, or it may be compared with the amount of transcription in asubstantially identical cell that lacks the T2R polypeptide. Asubstantially identical cell may be derived from the same cells fromwhich the recombinant cell was prepared but which had not been modifiedby introduction of heterologous DNA. Any difference in the amount oftranscription indicates that the test compound has in some manneraltered the activity of the T2R polypeptide of interest.

6. Transgenic Non-Human Animals Expressing Taste Receptors

Non-human animals expressing one or more T2R polypeptides of theinvention, can also be used for assays. Such expression can be used todetermine whether a test compound specifically binds to a mammalian T2Rpolypeptide in vivo by contacting a non-human animal stably ortransiently transfected with a nucleic acid encoding a T2R polypeptideor ligand-binding region thereof with a test compound, and determiningwhether the animal reacts to the test compound by specifically bindingto the polypeptide.

Animals transfected or infected with the vectors of the invention areparticularly useful for assays to identify and characterizetastants/ligands that can bind to a specific or sets of receptors. Suchvector-infected animals expressing human chemosensory receptor sequencescan be used for in vivo screening of tastants and their effect on, e.g.,cell physiology (e.g., on taste neurons), on the CNS, or behavior.

Means to infect/express the nucleic acids and vectors, eitherindividually or as libraries, are well known in the art. A variety ofindividual cell, organ, or whole animal parameters can be measured by avariety of means. The T2R sequences of the invention can be for exampleexpressed in animal taste tissues by delivery with an infecting agent,e.g., adenovirus expression vector.

The endogenous chemosensory receptor genes can remain functional andwild-type (native) activity can still be present. In other situations,where it is desirable that all chemosensory receptor activity is by theintroduced exogenous hybrid receptor, use of a knockout line ispreferred. Methods for the construction of non-human transgenic animals,particularly transgenic mice, and the selection and preparation ofrecombinant constructs for generating transformed cells are well knownin the art.

Construction of a “knockout” cell and animal is based on the premisethat the level of expression of a particular gene in a mammalian cellcan be decreased or completely abrogated by introducing into the genomea new DNA sequence that serves to interrupt some portion of the DNAsequence of the gene to be suppressed. Also, “gene trap insertion” canbe used to disrupt a host gene, and mouse embryonic stem (ES) cells canbe used to produce knockout transgenic animals (see, e.g., Holzschu,Transgenic Res, 6:97-106 (1997)). The insertion of the exogenous istypically by homologous recombination between complementary nucleic acidsequences. The exogenous sequence is some portion of the target gene tobe modified, such as exonic, intronic or transcriptional regulatorysequences, or any genomic sequence which is able to affect the level ofthe target gene's expression; or a combination thereof. Gene targetingvia homologous recombination in pluripotential embryonic stem cellsallows one to modify precisely the genomic sequence of interest. Anytechnique can be used to create, screen for, propagate, a knockoutanimal, e.g., see Bijvoet, Hum. Mol. Genet., 7:53-62 (1998); Moreadith,J. Mol. Med., 75:208-16 (1997); Tojo, Cytotechnology 19:161-165 (1995);Mudgett, Methods Mol. Biol. 48:167-184 (1995); Longo, Transgenic Res.6:321-328 (1997); U.S. Pat. Nos. 5,616,491; 5,464,764; 5,631,153;5,487,992; 5,627,059; 5,272,071; WO 91/09955; WO93/09222; WO 96/29411;WO 95/31560; WO 91/12650.

The nucleic acids of the invention can also be used as reagents toproduce “knockout” human cells and their progeny. Likewise, the nucleicacids of the invention can also be used as reagents to produce“knock-ins” in mice. The human or rat T2R gene sequences can replace theorthologous T2R in the mouse genome. In this way, a mouse expressing ahuman or rat T2R is produced. This mouse can then be used to analyze thefunction of human or rat T2Rs, and to identify ligands for such T2Rs.

F. Modulators

The compounds tested as modulators of a T2R family member can be anysmall chemical compound, or a biological entity, such as a protein,sugar, nucleic acid or lipid. Alternatively, modulators can begenetically altered versions of a T2R family member. Typically, testcompounds may be small chemical molecules and peptides. Essentially anychemical compound can be used as a potential modulator or ligand in theassays of the invention, although most often compounds can be dissolvedin aqueous or organic (especially DMSO-based) solutions are used. Theassays may be designed to screen large chemical libraries by automatingthe assay steps and providing compounds from any convenient source toassays, which are typically run in parallel (e.g., in microtiter formatson microtiter plates in robotic assays). It will be appreciated thatthere are many suppliers of chemical compounds, including Sigma (St.Louis, Mo.), Aldrich (St. Louis, Mo.), Sigma-Aldrich (St. Louis, Mo.),Fluka Chemika-Biochemica Analytika (Buchs, Switzerland) and the like.

In one embodiment, high throughput screening methods involve providing acombinatorial chemical or peptide library containing a large number ofpotential therapeutic compounds (potential modulator or ligandcompounds). Such “combinatorial chemical libraries” or “ligandlibraries” are then screened in one or more assays, as described herein,to identify those library members (particular chemical species orsubclasses) that display a desired characteristic activity. Thecompounds thus identified can serve as conventional “lead compounds” orcan themselves be used as potential or actual consumer products.

A combinatorial chemical library is a collection of diverse chemicalcompounds generated by either chemical synthesis or biologicalsynthesis, by combining a number of chemical “building blocks” such asreagents. For example, a linear combinatorial chemical library such as apolypeptide library is formed by combining a set of chemical buildingblocks (amino acids) in every possible way for a given compound length(i.e., the number of amino acids in a polypeptide compound). Millions ofchemical compounds can be synthesized through such combinatorial mixingof chemical building blocks.

Preparation and screening of combinatorial chemical libraries is wellknown to those of skill in the art. Such combinatorial chemicallibraries include, but are not limited to, peptide libraries (see, e.g.,U.S. Pat. No. 5,010,175, Furka, Int. J. Pept. Prot. Res., 37:487-93(1991) and Houghton et al., Nature, 354:84-88 (1991)). Other chemistriesfor generating chemical diversity libraries can also be used. Suchchemistries include, but are not limited to: peptoids (e.g., WO91/19735), encoded peptides (e.g., WO 93/20242), random bio-oligomers(e.g., WO 92/00091), benzodiazepines (e.g., U.S. Pat. No. 5,288,514),diversomers such as hydantoins, benzodiazepines and dipeptides (Hobbs etal., PNAS., 90:6909-13 (1993)), vinylogous polypeptides (Hagihara etal., J. Amer. Chem. Soc., 114:6568 (1992)), nonpeptidal peptidomimeticswith glucose scaffolding (Hirschmann et al., J. Amer. Chem. Soc.,114:9217-18 (1992)), analogous organic syntheses of small compoundlibraries (Chen et al., J. Amer. Chem. Soc., 116:2661 (1994)),oligocarbamates (Cho et al., Science, 261:1303 (1993)), peptidylphosphonates (Campbell et al., J. Org. Chem., 59:658 (1994)), nucleicacid libraries (Ausubel, Berger, and Sambrook, all supra), peptidenucleic acid libraries (U.S. Pat. No. 5,539,083), antibody libraries(Vaughn et al., Nature Biotechnology, 14(3):309-14 (1996) andPCT/US96/10287), carbohydrate libraries (Liang et al., Science,274:1520-22 (1996) and U.S. Pat. No. 5,593,853), small organic moleculelibraries (benzodiazepines, Baum, C&EN, January 18, page 33 (1993);thiazolidinones and metathiazanones, U.S. Pat. No. 5,549,974;pynrolidines, U.S. Pat. Nos. 5,525,735 and 5,519,134; morpholinocompounds, U.S. Pat. No. 5,506,337; benzodiazepines, U.S. Pat. No.5,288,514, and the like).

Devices for the preparation of combinatorial libraries are commerciallyavailable (see, e.g., 357 MPS, 390 MPS (Advanced Chem Tech, LouisvilleKy.), Symphony (Rainin, Woburn, Mass.), 433A (Applied Biosystems, FosterCity, Calif.), 9050 Plus (Millipore, Bedford, Mass.)). In addition,numerous combinatorial libraries are themselves commercially available(see, e.g., ComGenex, Princeton, N.J.; Tripos, Inc., St. Louis, Mo.; 3DPharmaceuticals, Exton, Pa.; Martek Biosciences; Columbia, Md.; etc.).

In one aspect of the invention, the T2R modulators can be used in anyfood product, confectionery, pharmaceutical composition, or ingredientthereof to thereby modulate the taste of the product, composition, oringredient in a desired manner. For instance, T2R modulators thatenhance bitter taste sensation can be added to provide a bitter taste toa product or composition, while T2R modulators which block bitter tastesensations can be added to improve the taste of a product orcomposition.

G. Methods for Representing and Predicting the Perception of Taste

The invention also preferably provides methods for representing theperception of taste and/or for predicting the perception of taste in amammal, including in a human. Preferably, such methods may be performedby using the receptors and genes encoding said T2R proteins disclosedherein.

Also contemplated as within the invention, is a method of screening oneor more compounds for the presence of a taste detectable by a mammal,comprising: contacting said one or more compounds with the disclosedreceptors, preferably wherein the mammal is a human. Also contemplatedas within the invention, is a method for representing taste perceptionof a particular taste in a mammal, comprising the steps of: providingvalues X₁ to X_(n) representative of the quantitative stimulation ofeach of n taste receptors of said vertebrate, where n is greater than orequal to 4; and generating from said values a quantitativerepresentation of taste perception. The taste receptors may be a tastereceptor disclosed herein, the representation may constitutes a point ora volume in n-dimensional space, may constitutes a graph or a spectrum,and may constitutes a matrix of quantitative representations. Also, theproviding step may comprise contacting a plurality ofrecombinantly-produced taste receptors with a test composition andquantitatively measuring the interaction of said composition with saidreceptors.

Also contemplated as within the invention, is a method for predictingthe taste perception in a mammal generated by one or more molecules orcombinations of molecules yielding unknown taste perception in a mammal,comprising the steps of: providing values X₁ to X_(n) representative ofthe quantitative stimulation of each of n taste receptors of saidvertebrate, where n is greater than or equal to 4, for one or moremolecules or combinations of molecules yielding known taste perceptionin a mammal; and generating from said values a quantitativerepresentation of taste perception in a mammal for the one or moremolecules or combinations of molecules yielding known taste perceptionin a mammal, providing values X₁ to X_(n) representative of thequantitative stimulation of each of n taste receptors of saidvertebrate, where n is greater than or equal to 4, for one or moremolecules or combinations of molecules yielding unknown taste perceptionin a mammal; and generating from said values a quantitativerepresentation of taste perception in a mammal for the one or moremolecules or combinations of molecules yielding unknown taste perceptionin a mammal, and predicting the taste perception in a mammal generatedby one or more molecules or combinations of molecules yielding unknowntaste perception in a mammal by comparing the quantitativerepresentation of taste perception in a mammal for the one or moremolecules or combinations of molecules yielding unknown taste perceptionin a mammal to the quantitative representation of taste perception in amammal for the one or more molecules or combinations of moleculesyielding known taste perception in a mammal. The taste receptors used inthis method may include a taste receptor disclosed herein.

In another embodiment, novel molecules or combinations of molecules aregenerated which elicit a predetermined taste perception in a mammal bydetermining a value of taste perception in a mammal for a known moleculeor combinations of molecules as described above; determining a value oftaste perception in a mammal for one or more unknown molecules orcombinations of molecules as described above; comparing the value oftaste perception in a mammal for one or more unknown compositions to thevalue of taste perception in a mammal for one or more knowncompositions; selecting a molecule or combination of molecules thatelicits a predetermined taste perception in a mammal; and combining twoor more unknown molecules or combinations of molecules to form amolecule or combination of molecules that elicits a predetermined tasteperception in a mammal. The combining step yields a single molecule or acombination of molecules that elicits a predetermined taste perceptionin a mammal.

In another embodiment of the invention, there is provided a method forsimulating a taste, comprising the steps of: for each of a plurality ofcloned taste receptors, preferably human receptors, ascertaining theextent to which the receptor interacts with the tastant; and combining aplurality of compounds, each having a previously-ascertained interactionwith one or more of the receptors, in amounts that together provide areceptor-stimulation profile that mimics the profile for the tastant.Interaction of a tastant with a taste receptor can be determined usingany of the binding or reporter assays described herein. The plurality ofcompounds may then be combined to form a mixture. If desired, one ormore of the plurality of the compounds can be combined covalently. Thecombined compounds substantially stimulate at least 75%, 80%, or 90% ofthe receptors that are substantially stimulated by the tastant.

In another preferred embodiment of the invention, a plurality ofstandard compounds are tested against a plurality of taste receptors toascertain the extent to which the receptors each interact with eachstandard compound, thereby generating a receptor stimulation profile foreach standard compound. These receptor stimulation profiles may then bestored in a relational database on a data storage medium. The method mayfurther comprise providing a desired receptor-stimulation profile for ataste; comparing the desired receptor stimulation profile to therelational database; and ascertaining one or more combinations ofstandard compounds that most closely match the desiredreceptor-stimulation profile. The method may further comprise combiningstandard compounds in one or more of the ascertained combinations tosimulate the taste.

H. Kits

T2R genes and their homologs are useful tools for identifying tastereceptor cells, for forensics and paternity determinations, and forexamining taste transduction. T2R family member-specific reagents thatspecifically hybridize to T2R nucleic acids, such as T2R probes andprimers, and T2R specific reagents that specifically bind to a T2Rprotein, e.g., T2R antibodies are used to examine taste cell expressionand taste transduction regulation.

Nucleic acid assays for the presence of DNA and RNA for a T2R familymember in a sample include numerous techniques are known to thoseskilled in the art, such as southern analysis, northern analysis, dotblots, RNase protection, S1 analysis, amplification techniques such asPCR, and in situ hybridization. In in situ hybridization, for example,the target nucleic acid is liberated from its cellular surroundings insuch as to be available for hybridization within the cell whilepreserving the cellular morphology for subsequent interpretation andanalysis. The following articles provide an overview of the art of insitu hybridization: Singer et al., Biotechniques, 4:230250 (1986); Haaseet al., Methods in Virology, vol. VII, 189-226 (1984); and Names et al.,eds., Nucleic Acid Hybridization: A Practical Approach (1987). Inaddition, a T2R protein can be detected with the various immunoassaytechniques described above. The test sample is typically compared toboth a positive control (e.g., a sample expressing a recombinant T2Rprotein) and a negative control.

The present invention also provides for kits for screening formodulators of T2R family members. Such kits can be prepared from readilyavailable materials and reagents. For example, such kits can compriseany one or more of the following materials: T2R nucleic acids orproteins, reaction tubes, and instructions for testing T2R activity.Optionally, the kit contains a functional T2R polypeptide. A widevariety of kits and components can be prepared according to the presentinvention, depending upon the intended user of the kit and theparticular needs of the user.

EXAMPLES

The following examples provide a summary of the isolated nucleic acidmolecules of the invention, and polypeptide sequences corresponding tothe conceptual translations of nucleic acid molecules. In the proteinsequences presented herein, the one-letter code X or Xaa refers to anyof the twenty common amino acid residues. In the DNA sequences presentedherein, the one letter codes N or n refers to any of the of the fourcommon nucleotide bases, A, T, C, or G.

hT2R51 Full-Length cDNA (BAC AC011654)(SEQ ID NO: 1) (SEQ ID NO: 1)ATGTTGACTCTAACTCGCATCCGCACTGTGTCCTATGAAGTCAGGAGTACATTTCTGTTCATTTCAGTCCTGGAGTTTGCAGTGGGGTTTCTGACCAATGCCTTCGTTTTCTTGGTGAATTTTTGGGATGTAGTGAAGAGGCAGGCACTGAGCAACAGTGATTGTGTGCTGCTGTGTCTCAGCATCAGCCGGCTTTTCCTGCATGGACTGCTGTTCCTGAGTGCTATCCAGCTTACCCACTTCCAGAAGTTGAGTGAACCACTGAACCACAGCTACCAAGCCATCATCATGCTATGGATGATTGCAAACCAAGCCAACCTCTGGCTTGCTGCCTGCCTCAGCCTGCTTTACTGCTCCAAGCTCATCCGTTTCTCTCACACCTTCCTGATCTGCTTGGCAAGCTGGGTCTCCAGGAAGATCTCCCAGATGCTCCTGGGTATTATTCTTTGCTCCTGCATCTGCACTGTCCTCTGTGTTTGGTGCTTTTTTAGCAGACCTCACTTCACAGTCACAACTGTGCTATTCATGAATAACAATACAAGGCTCAACTGGCAGATTAAAGATCTCAATTTATTTTATTCCTTTCTCTTCTGCTATCTGTGGTCTGTGCCTCCTTTCCTATTGTTTCTGGTTTCTTCTGGGATGCTGACTGTCTCCCTGGGAAGGCACATGAGGACAATGAAGGTCTATACCAGAAACTCTCGTGACCCCAGCCTGGAGGCCCACATTAAAGCCCTCAAGTCTCTTGTCTCCTTTTTCTGCTTCTTTGTGATATCATCCTGTGTTGCCTTCATCTCTGTGCCCCTACTGATTCTGTGGCGCGACAAAATAGGGGTGATGGTTTGTGTTGGGATAATGGCAGCTTGTCCCTCTGGGCATGCAGCCATCCTGATCTCAGGCAATGCCAAGTTGAGGAGAGCTGTGATGACCATTCTGCTCTGGGCTCAGAGCAGCCTGAAGGTAAGAGCCGACCACAAGGCAGATTCCCGGACACTGTGCTGA hT2R51 Conceptual Translation (BAC AC011654) (SEQ ID NO: 2)(SEQ ID NO: 2)MLTLTRIRTVSYEVRSTFLFISVLEFAVGFLTNAFVFLVNFWDVVKRQALSNSDCVLLCLSISRLFLHGLLFLSAIQLTHFQKLSEPLNHSYQAIIMLWMIANQANLWLAACLSLLYCSKLIRFSHTFLICLASWVSRKISQMLLGIILCSCICTVLCVWCFFSRPHFTVTTVLFMNNNTRLNWQIKDLNLFYSFLFCYLWSVPPFLLFLVSSGMLTVSLGRHMRTMKVYTRNSRDPSLEAMICALKSLVSFFCFFVISSCVAFISVPLLILWRDKIGVMVCVGIMAACPSGHAAILISGNAKLRRAVMTILLWAQSSLKVRADHKADSRTLC  hT2R54 Full-Length cDNA (BAC AC024156) (SEQ ID NO: 3)(SEQ ID NO: 3)ATGACTAAACTCTGCGATCCTGCAGAAAGTGAATTGTCGCCATTTCTCATCACCTTAATTTTAGCAGTTTTACTTGCTGAATACCTCATTGGTATCATTGCAAATGGTTTCATCATGGCTATACATGCAGCTGAATGGGTTCAAAATAAGGCAGTTTCCACAAGTGGCAGGATCCTGGTTTTCCTGAGTGTATCCAGAATAGCTCTCCAAAGCCTCATGATGTTAGAAATTACCATCAGCTCAACCTCCCTAAGTTTTTATTCTGAAGACGCTGTATATTATGCATTCAAAATAAGTTTTATATTCTTAAATTTTTGTAGCCTGTGGTTTGCTGCCTGGCTCAGTTTCTTCTACTTTGTGAAGATTGCCAATTTCTCCTACCCCCTTTTCCTCAAACTGAGGTGGAGAATTACTGGATTGATACCCTGGCTTCTGTGGCTGTCCGTGTTTATTTCCTTCAGTCACAGCATUITCTGCATCAACATCTGCACTGTGTATTGTAACAATTCTTTCCCTATCCACTCCTCCAACTCCACTAAGAAAACATACTTGTCTGAGATCAATGTGGTCGGTCTGGCTTTTTTCTTTAACCTGGGGATTGTGACTCCTCTGATCATGTTCATCCTGACAGCCACCCTGCTGATCCTCTCTCTCAAGAGACACACCCTACACATGGGAAGCAATGCCACAGGGTCCAACGACCCCAGCATGGAGGCTCACATGGGGGCCATCAAAGCTATCAGCTACTTTCTCATTCTCTACATTTTCAATGCAGTTGCTCTGTTTATCTACCTGTCCAACATGTTTGACATCAACAGTCTGTGGAATAATTTGTGCCAGATCATCATGGCTGCCTACCCTGCCAGCCACTCAATTCTACTGATTCAAGATAACCCTGGGCTGAGAAGAGCCTGGAAGCGGCTTCAGCTTCGACTTCATCTTTACCCAAAAGAGTGGACTCTGTGA hT2R54 Conceptual Translation (BAC AC024156) (SEQ ID NO: 4)(SEQ ID NO: 4)MTKLCDPAESELSPFLITLILAVLLAEYLIGIIANGFIMAIHAAEWVQNKAVSTSGRILVFLSVSRIALQSLMMLEITISSTSLSFYSEDAVYYAFKISFIFLNFCSLWFAAWLSFFYFVKIANFSYPLFLKLRWRITGLIPWLLWLSVFISFSHSMFCINICTVYCNNSFPIHSSNSTKKTYLSEINVVGLAFFFNLGIVTPLIMFILTATLLILSKRHTLHMGSNATGSNDPSMEAHMGAIKAISYFLILYIFNAVALFIYLSNMFDINSLWNNLCQIIMAAYPASHSILLIQDNPGLRRAWKRLQLRLHLYPKEWTL hT2R55 Full-Length cDNA (BAC AC024156) (SEQ ID NO: 5) (SEQ ID NO: 5)ATGGCAACGGTGAACACAGATGCCACAGATAAAGACATATCCAAGTTCAAGGTCACCTTCACTTTGGTGGTCTCCGGAATAGAGTGCATCACTGGCATCCTTGGGAGTGGCTTCATCACGGCCATCTATGGGGCTGAGTGGGCCAGGGGCAAAACACTCCCCACTGGTGACCGCATTATGTTGATGCTGAGCTTTTCCAGGCTCTTGCTACAGATTTGGATGATGCTGGAGAACATTTTCAGTCTGCTATTCCGAATTGTTTATAACCAAAACTCAGTGTATATCCTCTTCAAAGTCATCACTGTCTTTCTGAACCATTCCAATCTCTGGTTTGCTGCCTGGCTCAAAGTCTTCTATTGTCTTAGAATTGCAAACTTCAATCATCCTTTGTTCTTCCTGATGAAGAGGAAAATCATAGTGCTGATGCCTTGGCTTCTCAGGCTGTCAGTGTTGGTTTCCTTAAGCTTCAGCTTTCCTCTCTCGAGAGATGTCTTCAATGTGTATGTGAATAGCTCCATTCCTATCCCCTCCTCCAACTCCACGGAGAAGAAGTACTTCTCTGAGACCAATATGGTCAACCTGGTATTTTTCTATAACATGGGGATCTTCGTTCCTCTGATCATGTTCATCCTGGCAGCCACCCTGCTGATCCTCTCTCTCAAGAGACACACCCTACACATGGGAAGCAATGCCACAGGGTCCAGGGACCCCAGCATGAAGGCTCACATAGGGGCCATCAAAGCCACCAGCTACTTTCTCATCCTCTACATTTTCAATGCAATTGCTCTATTTCTTTCCACGTCCAACATCTTTGACACTTACAGTTCCTGGAATATTTTGTGCAAGATCATCATGGCTGCCTACCCTGCCGGCCACTCAGTACAACTGATCTTGGGCAACCCTGGGCTGAGAAGAGCCTGGAAGCGGTTTCAGCACCAAGTTCCTCTTTACCTAAAAGGGCAGACTCTGTGA hT2R55 Conceptual Translation (BAC AC024156) (SEQ ID NO: 6)(SEQ ID NO: 6)MATVNTDATDKDISKFKVTFTLVVSGIECITGILGSGFITAIYGAEWARGKTLPTGDRIMLMLSFSRLLLQIWMMLENIFSLLFRIVYNQNSVYILFKVITVFLNHSNLWFAAWLKVFYCLRIANFNHPLFFLMKRKIIVLMPWLLRLSVLVSLSFSFPLSRDVFNVYVNSSIPIPSSNSTEKKYFSETNMVNLVFFYNMGIFVPLIMFILAATLLILSLKRHTLHMGSNATGSRDPSMKAHIGAIKATSYFLILYIFNAIALFLSTSNIFDTYSSWNILCKIIMAAYPAGHSVQLILGNPGLRRAWKRFQHQVPLYLKGQTLhT2R61 Full-Length cDNA (BAC AC018630) (SEQ ID NO: 7) (SEQ ID NO: 7)ATGATAACTTTTCTACCCATCATTTTTTCCAGTCTGGTAGTGGTTACATTTGTTATTGGAAATTTTGCTAATGGCTTCATAGCACTGGTAAATTCCATTGAGTGGTTCAAGAGACAAAAGATCTCCTTTGCTGACCAAATTCTCACTGCTCTGGCGGTCTCCAGAGTTGGTTTGCTCTGGGTATTATTATTAAACTGGTATTCAACTGTGTTGAATCCAGCTTTTAATAGTGTAGAAGTAAGAACTACTGCTTATAATATCTGGGCAGTGATCAACCATTTCAGCAACTGGCTTGCTACTACCCTCAGCATATTTTATTTGCTCAAGATTGCCAATTTCTCCAACTTTATTTTTCTTCACTTAAAGAGGAGAGTTAAGAGTGTCATTCTGGTGATGTTGTTGGGGCCTTTGCTATTTTTGGCTTGTCATCTTTTTGTGATAAACATGAATGAGATTGTGCGGACAAAAGAATTTGAAGGAAACATGACTTGGAAGATCAAATTGAAGAGTGCAATGTACTTTTCAAATATGACTGTAACCATGGTAGCAAACTTAGTACCCTTCACTCTGACCCTACTATCTTTTATGCTGTTAATCTGTTCTITGTGTAAACATCTCAAGAAGATGCAGCTCCATGGTAAAGGATCTCAAGATCCCAGCACCAAGGTCCACATAAAAGCTTTGCAAACTGTGATCTCCTTCCTCTTGTTATGTGCCATTTACITTCTGTCCATAATGATATCAGTTTGGAGTTTTGGAAGTCTGGAAAACAAACCTGTCTTCATGTTCTGCAAAGCTATTAGATTCAGCTATCCTTCAATCCACCCATTCATCCTGATTTGGGGAAACAAGAAGCTAAAGCAGACTTTTCTTTCAGTTTTTTGGCAAATGAGGTACTGGGTGAAAGGAGAGAAGACTTCATCTCCATAG hT2R61 Conceptual Translation (BAC AC018630) (SEQ ID NO: 8)(SEQ ID NO: 8)MITFLPIIFSSLVVVTFVIGNFANGFIALVNSIEWFKRQKISFADQILTALAVSRVGLLWVLLLNWYSTVLNPAFNSVEVRITAYNIWAVINHFSNWLATTLSIFYLLKIANFSNFIFLHLKRRVKSVILVMLLGPLLFLACHLFVINMNEIVRTKEFEGNMTWKIKLKSAMYFSNMTVTMVANLVPFTLTLLSFMLLICSLCKHLICKMQLHGKGSQDPSTKVHIKALQTVISFLLLCAIYFLSIMISVWSFGSLENKPVFMFCKAIRFSYPSIHPFILIWGNKKLKQTFLSVFWQMRYWVKGEKTSSP hT2R63 Full-Length cDNA (BAC AC018630) (SEQ ID NO: 9) (SEQ ID NO: 9)ATGATGAGTTTTCTACACATTGTTTTTTCCATTCTAGTAGTGGTTGCATTTATTCTTGGAAATTTTGCCAATGGCTTTATAGCACTGATAAATTTCATTGCCTGGGTCAAGAGACAAAAGATCTCCTCAGCTGATCAAATTATTGCTGCTCTGGCAGTCTCCAGAGTTGGTTTGCTCTGGGTAATATTATTACATTGGTATTCAACTGTGTTGAATCCAACTTCATCTAATTTAAAAGTAATAATTTTTATTTCTAATGCCTGGGCAGTAACCAATCATTTCAGCATCTGGCTTGCTACTAGCCTCAGCATATTTTATTTGCTCAAGATCGTCAATTTCTCCAGACTTATTTTTCATCACTTAAAAAGGAAGGCTAAGAGTGTAGTTCTGGTGATAGTGTTGGGGTCTTTGTTCTTTTTGGTTTGTCACCTTGTGATGAAACACACGTATATAAATGTGTGGACAGAAGAATGTGAAGGAAACGTAACTTGGAAGATCAAACTGAGGAATGCAATGCACCTTTCCAACTTGACTGTAGCCATGCTAGCAAACTTGATACCATTCACTCTGACCCTGATATCTTTTCTGCTGTTAATCTACTCTCTGTGTAAACATCTGAAGAAGATGCAGCTCCATGGCAAAGGATCTCAAGATCCCAGCACCAAGATCCACATAAAAGCTCTGCAAACTGTGACCTCCTTCCTCATATTACTTGCCATTTACTTTCTGTGTCTAATCATATCGTTTTGGAATTTTAAGATGCGACCAAAAGAAATTGTCTTAATGCTTTGCCAAGCTTTTGGAATCATATATCCATCATTCCACTCATTCATTCTGATTTGGGGGAACAAGACGCTAAAGCAGACCTTTCTTTCAGTTTTGTGGCAGGTGACTTGCTGGGCAAAAGGACAGAACCAGTCAACTCCATAG  hT2R63 Conceptual Translation (BAC AC018630)(SEQ ID NO: 10)(SEQ ID NO: 10)MMSFLHIVFSILVVVAFILGNFANGFIALINFIAWYKRQKISSADQIIAALAVSRVGLLWVILLHWYSTVLNPTSSNLKVIIFISNAWAVTNHFSIWLATSLSIFYLLKIVNFSRLIFHHLKRKAKSVVLVIVLGSLFFLVCHLVMKHTYINVWTEECEGNVTWKIKLRNAMHLSNLTVAMLANLIPFTLTLISFLLLIYSLCKHLKKMQLHGKGSQDPSTKIHIKALQTVTSFLILLAIYFLCLIISFWNFKMRPKEIVLMLCQAFGIIYPSFHSFILIWGNKTLKQTFLSVLWQVTCWAKGQNQSTPhT2R64 Full-Length cDNA (BAC AC018630) (SEQ ID NO: 11) (SEQ ID NO: 11)ATGACAACTTTTATACCCATCATTTTTTCCAGTGTGGTAGTGGTTCTATTTGTTATTGGAAATTTTGCTAATGGCTTCATAGCATTGGTAAATTCCATTGAGCGGGTCAAGAGACAAAAGATCTCTTTTGCTGACCAGATTCTCACTGCTCTGGCGGTCTCCAGAGTTGGTTTGCTCTGGGTATTATTATTAAATTGGTATTCAACTGTGTTTAATCCAGCTTTTTATAGTGTAGAAGTAAGAACTACTGCTTATAATGTCTGGGCAGTAACCGGCCATTTCAGCAACTGGCTTGCTACTAGCCTCAGCATATTTTATTTGCTCAAGATTGCCAATTTCTCCAACCTTATTTTTCTTCACTTAAAGAGGAGAGTTAAGAGTGTCATTCTGGTGATGCTGTTGGGGCCTTTACTATTTTTGGCTTGTCAACTTTTTGTGATAAACATGAAAGAGATTGTACGGACAAAAGAATATGAAGGAAACTTGACTTGGAAGATCAAATTGAGGAGTGCAGTGTACCTTTCAGATGCGACTGTAACCACGCTAGGAAACTTAGTGCCCTTCACTCTGACCCTGCTATGTTTTTTGCTGTTAATCTGTTCTCTGTGTAAACATCTCAAGAAGATGCAGCTCCATGGTAAAGGATCTCAAGATCCCAGCACCAAGGTCCACATAAAAGCTTTGCAAACTGTGATCTTTTTCCTCTTGTTATGTGCCGTTTACTTTCTGTCCATAATGATATCAGTTTGGAGTTTTGGGAGTCTGGAAAACAAACCTGTCTTCATGTTCTGCAAAGCTATTAGATTCAGCTATCCTTCAATCCACCCATTCATCCTGATTTGGGGAAACAAGAAGCTAAAGCAGACTTTTCTTTCAGTTTTGCGGCAAGTGAGGTACTGGGTGAAAGGAGAGAAGCCTTCATCTCCATAG hT2R64 Conceptual Translation (BAC AC018630) (SEQ ID NO: 12)(SEQ ID NO: 12)MTTFIPIIFSSVVVVLFVIGNFANGFIALVNSIERVKRQKISFADQILTALAVSRVGLLWVLLLNWYSTVFNPAFYSVEVRTTAYNVWAVTGHFSNWLATSLSIFYLLKIANFSNLIFLHLKRRVKSVILVMLLGPLLFLACQLFVINMKEIVRTKEYEGNLTWKIKLRSAVYLSDATVTTLGNLVPFTLTLLCFLLLICSLCKHLKKMQLHGKGSQDPSTKVHIKALQTVIFFLLLCAVYFLSIMISVWSFGSLENKPVFMFCKAIRFSYPSIHPFILIWGNKKLKQTFLSVLRQVRYWVKGEKPSSP hT2R65 Full-Length cDNA (BAC AC018630) (SEQ ID NO: 13) (SEQ ID NO: 13)ATGATGTGTTTTCTGCTCATCATTTCATCAATTCTGGTAGTGTTTGCATTTGTICTTGGAAATGTTGCCAATGGCTTCATAGCCCTAGTAAATGICATTGACTGGGTTAACACACGAAAGATCTCCTCAGCTGAGCAAATTCTCACTGCTCTGGTGGTCTCCAGAATTGGTTTACTCTGGGTCATGTTATTCCTTTGGTATGCAACTGTGTTTAATTCTGCTTTATATGGTTTAGAAGTAAGAATTGTTGCTTCTAATGCCTGGGCTGTAACGAACCATTTCAGCATGTGGCTTGCTGCTAGCCTCAGCATATTTTGTTTGCTCAAGATTGCCAATTTCTCCAACCTTATTTCTCTCCACCTAAAGAAGAGAATTAAGAGTGTTGTTCTGGTGATACTGTTGGGGCCCTTGGTATTTCTGATTTGTAATCTTGCTGTGATAACCATGGATGAGAGAGTGTGGACAAAAGAATATGAAGGAAATGTGACTTGGAAGATCAAATTGAGGAATGCAATACACCTTTCAAGCTTGACTGTAACTACTCTAGCAAACCTCATACCCTTTACTCTGAGCCTAATATGTTTTCTGCTGTTAATCTGTTCTCTTTGTAAACATCTCAAGAAGATGCGGCTCCATAGCAAAGGATCTCAAGATCCCAGCACCAAGGTCCATATAAAAGCTTTGCAAACTGTGACCTCCTTCCTCATGTTATTTGCCATTTACTTTCTGTGTATAATCACATCAACTTGGAATCTTAGGACACAGCAGAGCAAACTTGTACTCCTGCTTTGCCAAACTGTTGCAATCATGTATCCTTCATTCCACTCATTCATCCTGATTATGGGAAGTAGGAAGCTAAAACAGACCTTTCTTTCAGTTTTGTGGCAGATGACACGCTGA hT2R65 Conceptual Translation (BAC AC018630) (SEQ ID NO: 14)(SEQ ID NO: 14)MMCELLIISSILVVFAFVLGNVANGFIALVNVIDWVNTRKISSAEQILTALVVSRIGLLWVMLFLWYATVFNSALYGLEVRIVASNAWAVTNHFSMWLAASLSIFCLLKIANFSNLISLHLKKRIKSVVLVILLGPLVFLICNLAVITMDERVWTKEYEGNVTWKIKLRNAIHLSSLTVTTLANLIPFTLSLICFLLLICSLCKHLKKMRLHSKGSQDPSTKVHIKALQTVTSFLMLFAIYFLCIITSTWNLRTQQSKLVLLLCQTVAIMYPSFHSFILIMGSRKLKQTFLSVLWQMTR hT2R67 Full-Length cDNA (BAC AC018630) (SEQ ID NO: 15) (SEQ ID NO: 15)ATGATAACTTTTCTATACATTTTTTTTTCAATTCTAATAATGGTTTTATTTGTTCTCGGAAACTTTGCCAATGGCTTCATAGCACTGGTAAATTTCATTGACTGGGTGAAGAGAAAAAAGATCTCCTCAGCTGACCAAATTCTCACTGCTCTGGCGGTCTCCAGAATTGGTTTGCTCTGGGCATTATTATTAAATTGGTATTTAACTGTGITGAATCCAGCTTTTTATAGTGTAGAATTAAGAATTACTTCTTATAATGCCTGGGTTGTAACCAACCATTTCAGCATGTGGCTTGCTGCTAACCTCAGCATATTTTATTTGCTCAAGATTGCCAATTTCTCCAACCTTCTTTTTCTTCATTTAAAGAGGAGAGTTAGGAGTGTCATTCTGGTGATACTGTTGGGGACTTTGATATTTTTGGTTTGTCATCTTCTTGTGGCAAACATGGATGAGAGTATGTGGGCAGAAGAATATGAAGGAAACATGACTGGGAAGATGAAATTGAGGAATACAGTACATCTTTCATATTTGACTGTAACTACCCTATGGAGCTTCATACCCTTTACTCTGTCCCTGATATCTTTTCTGATGCTAATCTGTTCTCTGTGTAAACATCTCAAGAAGATGCAGCTCCATGGAGAAGGATCGCAAGATCTCAGCACCAAGGTCCACATAAAAGCTTTGCAAACTCTGATCTCCTTCCTCTTGTTATGTGCCATTTTCTTTCTATTCCTAATCGTTTCGGTTTGGAGTCCTAGGAGGCTGCGGAATGACCCGGTTGTCATGGTTAGCAAGGCTGTTGGAAACATATATCTTGCATTCGACTCATTCATCCTAATTTGGAGAACCAAGAAGCTAAAACACACCTTTCTTTTGATTTTGTGTCAGATTAGGTGCTGA hT2R67 Conceptual Translation (BAC AC018630) (SEQ ID NO: 16)(SEQ ID NO: 16)MITFLYIFFSILIMVLFVLGNFANGFIALVNFIDWVKRKKISSADQILTALAVSRIGLLWALLLNWYLTVLNPAFYSVELRITSYNAWVVTNHFSMWLAANLSIFYLLKIANFSNLLFLHLKRRVRSVILVILLGTLIFLVCHLLVANMDESMWAEEYEGNMTGKMICLRNTVHLSYLTVTTLWSFIPFTLSLISFLMLICSLCKHLKKMQLHGEGSQDLSTKVHIKALQTLISFLLLCAIFFLFLIVSVWSPRRLRNDPVVMVSKAVGNIYLAFDSFILIWRTKKLKHTFLLILCQIRC hT2R71 Full-Length cDNA (BAC AC073264) (SEC) ID NO: 17) (SEQ ID NO: 17)ATGCAAGCAGCACTGACGGCCTTCTTCGTGTTGCTCTTTAGCCTGCTGAGTCTTCTGGGGATTGCAGCGAATGGCTTCATTGTGCTGGTGCTGGGCAGGGAGTGGCTGCGATATGGCAGGTTGCTGCCCTTGGATATGATCCTCATTAGCTTGGGTGCCTCCCGCTTCTGCCTGCAGTTGGTTGGGACGGTGCACAACTTCTACTACTCTGCCCAGAAGGTCGAGTACTCTGGGGGTCTCGGCCGACAGTTCTTCCATCTACACTGGCACTTCCTGAACTCAGCCACCTTCTGGTTTTGCAGCTGGCTCAGTGTCCTGTTCTGTGTGAAGATTGCTAACATCACACACTCCACCTTCCTGTGGCTGAAGTGGAGGTTCCCAGGGTGGGTGCCCTGGCTCCTGTTGGGCTCTGTCCTGATCTCCTTCATCATAACCCTGCTGTTTTTTTGGGTGAACTACCCTGTATATCAAGAATTTTTAATTAGAAAATTTTCTGGGAACATGACCTACAAGTGGAATACAAGGATAGAAACATACTATTTCCCATCCCTGAAACTGGTCATCTGGTCAATTCCTTTTTCTGTTTTTCTGGTCTCAATTATGCTGTTAATTAATTCTCTGAGGAGGCATACTCAGAGAATGCAGCACAACGGGCACAGCCTGCAGGACCCCAGCACCCAGGCTCACACCAGAGCTCTGAAGTCCCTCATCTCCTTCCTCATTCTTTATGCTCTGTCCTTTCTGTCCCTGATCATTGATGCCGCAAAATTTATCTCCATGCAGAACGACTTTTACTGGCCATGGCAAATTGCAGTCTACCTGTGCATATCTGTCCATCCCTTCATCCTCATCTTCAGCAACCTCAAGCTTCGAAGCGTGTTCTCGCAGCTCCTGTTGTTGGCAAGGGGCTTCTGGGTGGC CTAG hT2R71 Conceptual Translation (BAC AC073264) (SEQ ID NO: 18)(SEQ ID NO: 18)MQAALTAFFVLLFSLLSLLGIAANGFIVLVLGREWLRYGRLLPLDMILISLGASRFCLQLVGTVHNFYYSAQKVEYSGGLGRQFFHLHWHFLNSATFWFCSWLSVLFCVKIANITHSTFLWLKWRFPGWVPWLLLGSVLISFIITLLFFWVNYPVYQEFLIRKFSGNMTYKWNTRIETYYFPSLKLVIWSIPFSVFLVSIMLLINSLRRHTQRMQHNGHSLQDPSTQAHTRALKSLISFLILYALSFLSLIIDAAKFISMQNDFYWPWQIAVYLCISVHPFILIFSNLKLRSVFSQLLLLARGFWVA hT2R75 Full-Length cDNA (SEQ ID NO: 19) (SEQ ID NO: 19)ATGATAACTTTTCTGCCCATCATTTTTTCCATTCTAATAGTGGTTACATTTGTGATTGGAAATTTTGCTAATGGCTTCATAGCATTGGTAAATTCCATTGAGTGGTTCAAGAGACAAAAGATCTCTTTTGCTGACCAAATTCTCACTGCTCTGGCAGTCTCCAGAGTTGGTTTACTCTGGGTATTAGTATTAAATTGGTATGCAACTGAGTTGAATCCAGCTTTTAACAGTATAGAAGTAAGAATTACTGCTTACAATGTCTGGGCAGTAATCAACCATTTCAGCAACTGGCTTGCTACTAGCCTCAGCATATTTTATTTGCTCAAGATTGCCAATTTCTCCAACCTTATTTTTCTTCACTTAAAGAGGAGAGTTAAGAGTGTTGITCTGGTGATACTATTGGGGCCTTTOCTATTTTTGGTTTGTCATCTTTTTGTGATAAACATGAATCAGATTATATGGACAAAAGAATATGAAGGAAACATGACTTGGAAGATCAAACTGAGGAGTGCAATGTACCITTCAAATACAACGGTAACCATCCTAGCAAACTTAGTTCCCTTCACTCTGACCCTGATATCTTTTCTGCTGTTAATCTGTTCTCTGTGTAAACATCTCAAAAAGATGCAGCTCCATGGCAAAGGATCTCAAGATCCCAGCATGAAGGTCCACATAAAAGCTTTGCAAACTGTGACCTCCTTCCTCTTOTTATGTGCCATTTACTTTCTOTCCATAATCATGTCAGTTTGGAGTTTTGAGAGTCTGGAAAACAAACCTGTCTTCATGTTCTGCGAAGCTATTGCATTCAGCTATCCTTCAACCCACCCATTCATCCTGATTTGGGGAAACAAGAAGCTAAAGCAGACTTTTCTTTCAGTTTTGTGGCATGTGAGGTACTGGGTGAAAGGAGAGAAGCCTTCATCTTCATAG  hT2R75 Conceptual Translation (SEQ ID NO: 20)(SEQ ID NO: 20)MITFLPIIFSILIVVTFVIGNFANGFIALVNSIEWFKRQKISFADQILTALAVSRVGLLWVLVLNWYATELNPAFNSIEVRITAYNVWAVINHFSNWLATSLSIFYLLKIANFSNLIFLHLKRRVKSVVLVILLGPLLFLVCHLFVINMNQIIWTKEYEGNMTWKIKLRSAMYLSNTTVTILANLVPFTLTLISFLLLICSLCKHLICKMQLHGKGSQDPSMKVHIKALQTVTSFLLLCAIYFLSIIMSVWSFESLENKPVFMFCEAIAFSYPSTHPFILIWGNKKLKQTFLSVLWHVRYWVKGEKPSSS hT2R59 Pseudogene (BAC AC018630) (SEQ ID NO: 21) (SEQ ID NO: 21)ATGGTATATTTTCTGCTCATCATTTTATCAATTCTGGTAGTGTTTGCATTTGTTCTTGGAAATTTTTCCAATGGCTTCATAGCTCTAGTAAATGTCATTGACTGGGTTAAGACACGAAAGATCTCCTCAGCTGACCAAATCCTCACTGCTCTGGTGGTCTCCAGAATTGGTTACTCTGGGTCATATTATTACATTGGTATGCAAATGTGTTTAATTCAGCTTTATATAGTTCAGAAGTAGGAGCTGTTGCTTCTAATATCTCAGCAATAATCAACCATTTCAGCATCTGGCTTGCTGCTAGCCTCAGCATATTTTATTTGCTCAAGATTGCCAATTTCTCCAACCTTATTTTTCTCCACCTAAAGAAGAGAATTAGGAGTGTTGTTCTGGTGATACTGTTGGGTCCCTTGGTATTTTTGATTTGTAATCTTGCTGTGATAACCATGGATGACAGTGTGTGGACAAAAGAATATGAAGGAAATGTGACTTGGAAGATCAAATTGAGGAATGCAATACACCTTTCAAACTTGACTGTAAGCACACTAGCAAACCTCATACCCTTCATTCTGACCCTAATATGTTTTCTGCTGTTAATCTGTTCTCTGCATAAACATCTCAAGAAGATGCAGCTCCATGGCAAAGGATCTCAAGATCTCAGCACCAAGGTCCACATAAAAGCTTTGCAAACTGTGATCTCCTTCCTCATGTTATATGCCATTTACTTTCTGTATCTAATCACATTAACCTGGAATCTTTGAACACAGCAGAACAAACTTGTATTCCTGCTTTGCCAAACTCTTGGAATCATGTATCCTTCATTCCACTCATTCTTCCTGATTATGGGAAGCAGGAAACTAAAACAGACGTTTCTTTCAGTTTTATGTCAGGTCACATGCTTAGTGAAAGGACAGCAACCCTCAACTCCATAG  hT2R69 Pseudogene (BAC AC018630) (SEQ ID NO: 22)(SEQ ID NO: 22)ATGATATGTTTTCTGCTCATCATTTTATCAATTCTGGTAGTGTTTGCATTTGTTCTTGGAAATGTTGCCAATGGCTTCATAGCTCTAGTAGGTGTCCTTGAGTGGGTTAAGACACAAAAGATCTCATCAGCTGACCAAATTTCTCACTGCTCTGGTGGTGTCCAGAGTTGGTTTACTCTGGGTCATATTATTACATTGGTATGCAACTGTGTTTAATTTGGCTTCACATAGATTAGAAGTAAGAATTTITGGTTCTAATGTCTCAGCAATAACCAAGCATTTCAGCATCTGGGTGTTACTAGCCTCAGCATATTTCATTTGCTCAAGACTGCCAATTTCTCCAACCTTATTTTTCTCCACCTAAAGAAAAGGATTAAGAATGTTGGTTTGGTGATGGTGTTGGGGCCCTTGGTATTTTTCATTTGTAATCTTGCTCTGATAACCACGGGTGAGAGTGTGTGGACAAAAGAATATGAAGGAAATTTGTCTTGGATGATCAAATTGAGGAATGCAATACAGCTTTCAAACTTGACTGTAACCATGCCAGCAAACGTCACACCCTGCACTCTGACACTAATATCTTTTCTGCTGTTAATCTATTCTCCATGTAAACATGTCAAGAAGATGCAGCTCCATGGCAAAGGATCTCAACATCTCAGCACCAAGGTGCACATAAAAGCTTTGCAAACTGTGATCTCCTTCCTTATGTTATTTGCCATTTACTTTCTGTGTCTAATCACATCAACITGGAATCCTAGGACTCAGCAGAGCAAACTTGTATTCCTGCTTTACCAAACTCTTGGATTCATGTATCTTTTGTTCCACTCATTCATCCTGACTATGGGAAGTAGGAAGCCAAAACAGACCTTTCTTTCAGCTTTGTGA mT2R33 Full-Length cDNA (BAC ACO20619) (SEQ ID NO: 23) (SEQ ID NO: 23)ATGACCTCCCCTTTCCCAGCTATTTATCACATGGTCATCATGACAGCAGAGTTTCTCATCGGGACTACAGTGAATGGATTCCTTATCATTGTGAACTGCTATGACTTGTTCAAGAGCCGAACGTTCCTGATCCTGCAGACCCTCTTGATGTGCACAGGGCTGTCCAGACTCGGTCTGCAGATAATGCTCATGACCCAAAGCTTCTTCTCTGTGTTCTTTCCATACTCTTATGAGGAAAATATTTATAGTTCAGATATAATGTTCGTCTGGATGTTCTTCAGCTCGATTGGCCTCTGGTTTGCCACATGTCTCTCTGTCTTTTACTGCCTCAAGATTTCAGGCTTCACTCCACCCTGGTTTCTTTGGCTGAAATTCAGAATTTCAAAGCTCATATTTTGGCTGCTTCTGGGCAGCTTGCTGGCCTCTCTGGGCACTGCAACTGTGTGCATCGAGGTAGGTTTCCCTTTAATTGAGGATGGCTATGTCCTGAGAAACGCAGGACTAAATGATAGTAATGCCAAGCTAGTGAGAAATAATGACTTGCTCCTCATCAACCTGATCCTCCTGCTTCCCCTGTCTGTGTTTGTGATGTGCACCTCTATGTTATTTGTTTCTCTTTACAAGCACATGCACTGGATGCAAAGCGAATCTCACAAGCTGTCAAGTGCCAGAACCGAAGCTCATATAAATGCATTAAAGACAGTGACAACATTCTTTTGTTTCTTTGTTTCTTACTTTGCTGCCTTCATGGCAAATATGACATTTAGAATTCCATACAGAAGTCATCAGTTCTTCGTGGTGAAGGAAATCATGGCAGCATATCCCGCCGGCCACTCTGTCATAATCGTCTTGAGTAACTCTAAGTTCAAAGACTTATTCAGGAGAATGATCTGTCTACAGAAGGAAGAGTGA mT2R33 Conceptual Translation (BAC AC020619) (SEQ ID NO: 24)(SEQ ID NO: 24)MTSPFPAIYHMVIMTAEFLIGTTVNGFLIIVNCYDLFKSRTFLILQTLLMCTGLSRLGLQIMLMTQSFFSVFFPYSYEENIYSSDIMFVWMFFSSIGLWFATCLSVFYCLKISGFTPPWFLWLKFRISKLIFWLLLGSLLASLGTATVCIEVGFPLIEDGYVLRNAGLNDSNAKLVRNNDLLLINLILLLPLSVFVMCTSMLFVSLYKHMHWMQSESHKLSSARTEAHINALKTVTTFFCFFVSYFAAFMANMTFRIPYRSHQFFVVKEIMAAYPAGHSVIIVLSNSKFKDLFRRMICLQKEE 

While the foregoing detailed description has described severalembodiments of the present invention, it is to be understood that theabove description is illustrative only and not limiting of the disclosedinvention. The invention is to be limited only by the claims whichfollow.

What is claimed:
 1. A composition comprising a recombinant cell engineered to express a polypeptide that possesses at least 90% sequence identity to the bitter taste receptor polypeptide of SEQ ID NO: 6, wherein said composition further comprises an agent that facilitates the detection of compounds which modulate the signal transduction activity of said polypeptide.
 2. The composition of claim 1 wherein the polypeptide possesses at least 95% sequence identity to the bitter taste receptor polypeptide of SEQ ID NO:
 6. 3. The composition of claim 1 wherein the polypeptide that possesses at least 98% sequence identity to the bitter taste receptor polypeptide of SEQ ID NO:
 6. 4. The composition of claim 1 wherein the polypeptide possesses at least 99% sequence identity to the bitter taste receptor polypeptide of SEQ ID NO:6.
 5. The composition of claim 1 wherein the polypeptide is at identical to the bitter taste receptor polypeptide of SEQ ID NO:
 6. 6. The composition of claim 1 wherein the agent detects the effect of a compound on intracellular sodium, calcium, cAMP, cGMP or IP3.
 7. The composition of claim 1 wherein the agent is a calcium or sodium specific fluorescent dye.
 8. The composition of claim 1 wherein the agent is a voltage dye.
 9. The composition of claim 1 wherein the agent is selected from Fluo-3, Fluo-4 and Fura-2.
 10. The composition of claim 1, wherein the cell further expresses a chimeric G protein that couples to said polypeptide.
 11. The composition of claim 1, wherein the cell is engineered to express a G protein that couples to said polypeptide selected from Gα15 and Gα16. 